JP Pistons in Oztralia is one possible source for pistons. They are quite widely used here, to good reports. I've not needed to have tried them, yet. Although some reports have them as being a bit heavy, and they need good clearance.
Measure and weigh your existing piston, and make sure they supply something suitable. JP 1032 looks like what you want, make sure you check with them it will be the same. And make sure its rebored with plenty of clearance, too tight is not good. Typical watercooled clearances will cause trouble.... hth.
Alan, Y'don't say what over size you are at, or want to find?
You might try to find who bought out Domi Racer, MAYBE they may still have a wire wound piston the size you want.....
I bought a .020" over wire wound piston from Domi, just before they closed for ever..... I will need to find rings, circlips, and a wrist pin when I get to the point I need it. Brett
P.S. .... I don't know if anyone keeps their "worn out" pistons, but maybe, if you ask, someone might have a "worn out" piston of the size you need to go to, ask your machinist if they can set up to bore to a worn piston, wire wound or otherwise, to the clearance it needs, once you have the worn piston in hand, so the cylinder and piston can be handed to the machinist.
Like, I have ONE .030" over BSA A65 piston, I'd SURE like to find another usable one to match. No cracks or smears... Or other damage...