You can just get any white PBT key set and throw them on. Any size kit you buy will work
That may be true for a poker, but the pure has an extra key, and a shorter right shift. If you get blank, or something different (like up arrow) for the extra key, it'll work, but I don't know if a normal full set would have the short right shift. I guess you could put a 1x key on there, but you might have to order one in that size from SP or something.
Other than that, I believe it should be pretty easy to get the rest of the keys to work from any normal PBT set.