Vertex, Wossner, Wiseco ... They'd be available through all.
Generally though you just buy a complete piston kit which comes with pin, clips, rings and piston. Then I grab a new small end bearing just for good measure. FWW, the stock GG pistons are actually Vertex.
Jakobi, yep that's exactly what I was asking: I have everything but the small end bearing (aka wrist pin bearing).
rxmx - Great! Thanks. I'd read 18x22x22, which is the same as that Wiseco part. Just ordered one from amazon for $16, including shipping.
I love my GG, but you gotta think outside the box when sourcing parts sometimes It's not like my girlfriend's KDX220 where I can hit one site and get everything I need (and more easily compare prices as well.)