Thanks for all the input, everyone!
What I'm hearing, generally, is that people who tend to prefer BS keyboards are ... well, more "conservative" -- putting an Iron Man LED-lit keycap on a SSK would be like putting spinning rims on a classic muscle car -- morally wrong on some level. I spent about an hour looking for some kind of logo, shape or icon that would be in keeping with the vintage character of those keyboards and, well, I came up empty. We don't pimp out our 'boards.
Some choice comments picked out:
It's because nobody can manufacture custom stuff for buckling springs. SP doesn't deal in BS at all, and Unicomp's custom stuff has looked pretty bad in the past. I remember seeing an old order thread for red "GEEK HACK" keys manufactured by Unicomp that were all off-center and uneven.
I'm reworking a 122-key terminal keyboard into a more standardized Model M configuration, so I bought a whole new set of keys from Unicomp. They fit, but I had one or two keys out of the bunch that were a bit splayed out. The caps connect to the stems, but flare out a bit at the bottoms and interfere with the neighboring keys. Couple that with your experience hashbaz and I guess they wouldn't be the right supplier. Anyone have any experience with FenTek? They offer colored keycaps for buckling spring keyboards, but I've never bought anything from them.
Actually, I could see it being simpler to do some exotic stuff for a buckling-spring board because there's no profile issues-- alll caps the same height. But they'd almost have to be done as two-part key tops, due to the complexities of the bottom half of a BS key.
I didn't think the BS keycaps were particularly complex. The uppermost keycap connects to the stem with just two ridges on the sides. Seems a lot simpler to me than the cross shape seen on Cherry keycaps. I have no Cherry keyboards at all, but they seem like they would more complicated to mold, no?
But yes, 0100010 hit the nail on the head. Other than maybe a blank colored keycap or two, or the Black/Gray/Green sets, most of us who favor buckling spring also pretty much drive these things into the ground. (Well okay, maybe that's just me.) We largely buy 'em because they are damn near indestructible and we use them constantly. We're not looking for flashy shiny pretty thing - though I'd personally love a side-printed set - we're looking for a very sturdy tool to get the job done.
Side printed... that would be different (well not SO DIFFERENT, because some of the original BS keycaps are side printed, aren't they side printed on the SSK? What were the original Model M keycaps made out of? ABS? PBT? Does it even matter? As for black keycaps with black print, that shouldn't be impossible. I'll email the people at SP and see what they say.