I thought I would provide you with some additional information, since I am very familiar with the topic.
SWITCHES
Custom switches for MX keyboards came in several stages.
Stage 0. The Beginning.
These were the original Cherry "tactiles:" MX Clear, and later MX Brown.
Stage 1. Modded Cherry tactiles.
People performed their own mods to Cherry's original tactiles, circa 2011-12. Not many springs were available.
The most popular were Ergo Clears, using stock Cherry MX Black, Blue, or Brown springs.
Later Korean springs allowed dedicated 62, 55, and 63.5 G springs for Ergo Clears.
People also experimented with what became the common 3203, 3204 and 205g0 lubes.
People seemed to be looking for a switch more tactile than MX Brown, but lighter than MX Clear. Ergo Clears achieved this for some people.
Stage 2. Clones
Chinese clone manufacturers produced their own versions of Cherry's MX lineup. But they didn't offer much different. Gateron became popular, as their Browns seemed to be smoother than MX Browns. And there was some mixing of parts between them.
Also, some people prefer Browns from different manufacturers, such as OUTEMU or Gaote.
MX Clears were not copied as much, so did not give rise to new Ergo Clear variants.
Stage 3. Kailh and Zeal
Around 2016-2018 or so, Zeal and then Kailh offered some actually new tactile designs.
I'll start with Kailh. They went beyond their clone lineup and produced some new designs, their BOX housing being the most prominent.
The Kailh BOX housing is interesting, because it is not Cherry. It is not simply a copy of MX. It is a boxy housing that's allegedly dust-resistant. Theoretically, it can be more stable than Cherry. But their manufacturing often isn't much better than Cherry's, so it doesn't matter. Although BOX Reds were smoother than Cherry reds.
BOX clickies are very interesting, and generally more liked than MX Blue. But they also made some tactiles based on their BOX housing:
-BOX Brown: This is a fairly tactile "light tactile" that has resistance more at the top than MX Brown. It feels less like a Brown-style near-linear and more like an old-style pre-MX tactile. It's crunchier, and the drop is more noticeable. They feel more authoritative, more type-writer like.
-BOX Orange: This is just a BOX Brown with a heavier spring. It's worse IMHO, because the heavier spring means less tactility and more pointless weight.
-BOX Royal: a later, perhaps absurdly tactile switch.
-There was also a sort-of clone of Kailh BOX tactiles that were made to be like Ergo Clears. The Hako switches. I think it was Hako Violet. They haven't been talked about in a while. An interesting alternative to Kailh BOX Brown.
BTW, the early Kailh BOX switches broke keycaps, especially GMK. Never use pre-retool BOX switches. Never put GMK on any BOX switches. I don't trust them for that, no matter what people say.
Also, people say that all Kailh tactiles turn clicky eventually, once the lube in a certain area runs out. I don't think it's such a big problem, since BOX tactiles are noisy anyway. But some people really hate it.
Kailh also made more conventional MX-style switches that were still different, notably:
-Kailh Speed Copper: This is like an MX Brown, but the tactile barrier is right at the top, then it just collapses. So it's kinda like a click-less clicky. Very crisp.
-Kailh Pro Purple: This is a Brown or light Ergo-Clear where the tactile barrier is at the top instead of the middle. You can have fun with these, put in 3204 and 63.5 G Spirit springs.
Okay, so that's Kailh.
Around the same time, people here were getting Gateron to produce a custom line. The purpose was to create a factory Ergo Clear, that was also better than Ergo Clears.
So that became Zeal, and the switch is known as Zealio V1. It's back as the Zealio V1 Redux.
They aren't quite as tactile as the old MX Clears, I think. But they are definitely smoother than modern Clears. You can get them in multiple weights.
Because Zealios were successful, it led to the development of further custom switches by Zeal and others.
Stage 4 - The Heavy Tactiles
As custom switches progressed, people found that they wanted smoother linears, more clicky clickies, and more tactile tactiles.
The success of Zealio V1 led to Zealio V2, which is a very different switch.
Zealio V2 has a much larger tactile bump that is higher up. The tactile bump is so large than you can hit it and 'hang,' before actually actuating the switch.
At the same time, the so-called "Holy Panda" had become very popular.
It was a mixture of the YOK Panda housing, a mediocre linear, and the stem of a Halo True.
The Halo True is one of those Kailh/Hako style switches, I think it may have been commissioned by Drop or something. It's a tactile somewhat in the vein of MX Clear: it has a medium-sized bump, and a heavy spring that becomes progressively heavier.
Some people like Halo True on its own. But most people liked what is known as this 'frankenswitch,' where two or more switches are combined to form a new one, in this case the Holy Panda.
The Holy Panda has a large, satisfying bump that is fairly round instead of sharp. It can feel like a giant MX Brown, if built that way.
Anyway, these switches were going for $5.00 each, at one point. But several manufacturers and distributors stepped in to provide parts. And there are many clones of it today. The Holy Panda became the "Ergo Clear" sensation of 2018 or so.
Stage 5 - Plethora of switches
During 2018-2019 to the beginning of the pandemic, you basically had the Kailh lineup of tactiles to choose from, along with heavy tactiles like Zealio V2 and Holy Panda.
But a lot of manufacturers stepped in at that point. Durock emerged to produce the T1, which is a 'heavy' or 'medium-heavy' tactile styled after Zeal V2 and Holy Panda. It's a bit more restrained and rounded. Factory sound is very middling, and needs lube.
Durock later came up with the "Durock Medium Tactile," which is closer to the Zealio V1 and Ergo Clear. There were many recolours, from MODE Signal to Penguin and Taro Ball. I think RARA was the first of these, but I'm not sure.
AKKO CS emerged as a low-cost manufacturer. The CS Ocean Blue and Purple switches are widely-praised for being affordable medium tactiles that kind of feel like lesser Holy Pandas.
Meanwhile, OUTEMU had refined its custom offerings. It had started around the Kailh / Zeal V1 era to produce the OUTEMU Sky, an attempt at a factory Ergo Clear. The stem was actually pretty good, although it changed over time. The housings were really bad, though.
Later, they came up with the U4 Boba, a wildly-popular silent heavy-tactile. It is the closest MX switch to EC switches like Topre, or especially Niz.
From the Boba, they developed the U4T. The T in the U4T stands for "Thock." It is a loud version of the U4 Boba, using a long-stem. Long-stemmed switched had become popular since the Holy Panda.
The U4T is beloved because it uses the excellent Boba housing, which is smoother, better-sounding, more tactile, and more stable than Cherry. The U4T is about as tactile as a Holy Panda, or especially a T1.
So if you are looking for a particularly thocky and good heavy-tactile, try U4T. It isn't that heavy. You can also build them at 55 G with lube, and they are pretty tame.
RECOMMENDATIONS
You need a 104-key board. Problem is: people who funded custom keyboards in the past 5 years did not want full-size keyboards. They barely even want TKLs. Most custom kits are in the 60-75% range. And the TKLs are expensive.
So what you probably will end up having to do is get a factory 104/108-key board, have the switches taken out by desoldering, and then resolder in the switches you want.
As I said earlier, the best board for that purpose is the Leopold FC900R PD.
I can tell you right now, no factory MX board is adequate. They all have problems. Some of which you can fix with new switches and lubing the stabilizers.
But they all use the inferior tray-mount setup, which produces uneven sound, mediocre feel, and perhaps more ping. But what can you do? The only custom parts I know of are several GBs for custom Filco TKL PCBs and plates. I guess that's the best you can do.
So you are stuck with tray-mount. But at least you can get some decent switches into there. Some builds I know of: Zilent V2, Ergo Clear, Holy Panda. These have been done in factory full-size.
If I were you, I would get ahold of some samples of the following switches:
U4T Boba [probably 62 G], Holy Panda, Durock T1 [or JWick T1], SP Star Purple, Lilac tactile, maybe SP Star Dark "Magic Girl," and especially lubed Kiwi if you can get it.
Try them out in hand or in hot-swap. You only need 10 or less of each.
How to get: You can order from the individual stores, which is expensive. Or you can pandle on r/mechmarket, as people sell their used [often lubed] switches, or straight up beg there as people have excess switches.
Also, there are people who will assemble like 20 different individual samples in a bag for you, which is the best option.
Anyway, get ahold of samples or go to a meetup. Don't build anything without having tried samples.
Trust me.
Then you pay a service to do the whole desoldering / resoldering thing. Unless you have experience.
That's why I say, Leopold FC900R PD with U4T might save you a lot of time and trouble. At least with a pre-built, you don't need to buy more parts, and can just lube the existing stabilizers. Then, you're set.
A dark horse option is the Varmilo custom store. It's the closest thing to what you asked for: somewhere you can just buy a factory 'custom' keyboard.
I had a good experience with them back in 2018, but don't know what their shipping and reliability is like after the pandemic.
You can get a full-size Varmilo 108-key board with their excellent keycaps [even a custom pattern you select!] + Zealio V2 67 G switches from the store. Which is kinda incredible. Ask them to clip + lube the stabilizers while they are at it. It is the very best 'factory' experience for sure, if it goes well.
But in truth, I wouldn't buy or use any factory keyboard without lubing the switches. So that kinda negates Varmilo and their unlubed switches. Sure, Zeal switches are smooth from factory, but lube helps their sound, and their springs need lube or replacement for sure. So you're not getting the optimum experience from Varmilo, since their switches are unlubed.
You can actually get away with unlubed U4T, sort of like with Zeal, but still the springs at the very least should be lubed.
Another option is just to buy a Topre PFU edition or Realforce V3, in your preferred weight.
