Designing a case for CNC manufacturing is not a trivial task at all.
It is in fact the most tricky part of keyboard design.
As an example I already designed and manufactured two keyboards for my personal use and in the way of designing a third one.
The PCB design and soldering part became something quite easy for me to achieve, and far less challenging.
Designing a case on Fusion360 on the other hand is another topic...
First you are tied to inherent limitations of keyboard mechanics, that is the plate, the PCB and other components that must fit into your case with no problem.
This limit a lot your design possibilities and make things harder to make a nice good looking case at the end.
That's not without reasons people often say "Yep, yet another rectangle..." or "Nice rectangle!", because you are tied with the fact that all important mechanical parts are in a rather big rectangle to begin with.
Second, you have to design something that is machinable by a CNC shop and there are a lot of limitations to make that possible.
I had to read countless time 3dHubs, Xometry and other online shops document to kind of understand what they are requesting.
Also to document myself quite a bit on how CNC machining is done on various kind of machines (3 axis, 4 axis, 5 axis).
Third, CNC manufacturing is crazy expensive for a one off.
As a personnal example, made my 2 first designs made in EU:
- around 600€ for 1 unit of the first design.
- around 2000€ for 3 units of the second one.
- sure in China it may be cheaper, but you have the idea.
So you must not make ANY design mistakes if you want to have the chance of something that assemble correctly (and works correctly).
Yet having something that also feel and sound correctly is another difficulty on top of that.
As you see, case design a a pretty tedious, time consuming and nerve breaking process.
I'm not sure you'll find someone nice enough to do that kind of work for free (or cheap).
So my guess is, do as some people willing to have their own stuff, learn Fusion360 (or another CAD software) and do that yourself.
This will not come without tremendous effort, but in the end it is very rewarding