is ARH
http://www.airrifleheadquarters.com
He hasn't had his DIY stocks on his site for a few months, but there are unconfirmed rumors that he will again. I believe he used to sell thumbhole RWS34 stocks. If you are serious about buying one, you could always email him.
He also sells springs, spring kits with fitted guides, piston seals, lubricants and other goodies.
There are a few other airgun stockmakers such as Dave G. at
http://davegstocks.blogspot.com/ , Jan Kraner, Mike Abernathy, Steve Corcoran at
http://www.woodsandwateroutdoors.com/ , and maybe others.
Good luck,
--
Dan (in NY)