I've found a few typewriters at a nearby thrift store that have interesting caps, but the mountings are odd.
The brands are brother and olympus-some have semi-circles that could be modified, I expect, one has (i think) neat keys, but slits, that could maybe be dremmeled into plusses for cherrys, or something, and the olympus has plusses that look like they might fit cherrys with no modding-but it also doesn't have such spherical keys, more like there's a rounded line in from each corner, that meet at the lowest point in the middle.
All double shot, with a few tripple, although those are mostly typewriter stuff that few people would wont on computer keyboards.
Worth it, maybe? they're a few bucks, could probably offer ten for all 4. But then I have to put many pounds in my pile of electronics for recycling, which is a serious negative.