There are all sorts of keycaps out there on old boards, even old genuine Cherry boards can have dyesubbed PBT, lasered POM or PBT, pad printed ABS or doubleshot ABS.
Any of the sets found on Cherry G80-3000 or G81-3000 boards will fit, but it's sometimes hard to tell which ones are which materials unless you have the full product id. If you do, then you can look up here:
http://deskthority.net/wiki/Cherry_article_numbers#KeycapsThat will at least tell you what type of legend is on the caps. For material, if they're black and lasered, they're POM, if they're light coloured and lasered, they're PBT.
For instance, a G80-3000LQCEU-2 with light coloured keycaps has lasered PBT caps, Clear switches and EU ANSI layout.
In terms of original cherry boards, abs is what you will usually get
A board with PBT cherry caps is usually upwards of $500 if the seller knows the proper value.
I disagree.. I happen to have 2 G80-3000 boards with PBT caps which I bought new for 60 euro each. They have the newer, thin lasered PBT caps, though, but even a board with thick Cherry PBT shouldn't cost
that much.
I believe this set should fit, too:
https://geekhack.org/index.php?topic=68198.0As should this one if you get the Specialty Kit, ISO kit and Numpad kit:
https://geekhack.org/index.php?topic=65935.0