You might try Pacific Heat Treating. I got their name from one of my books on knife making (sorry, I can't remember the authors of the book for proper credit), I think it was "How to make knives". I have used them for 3 or 4 years on some O-1 stock removal knives, and they have done excellent work for me.
Their address is:
Pacific Heat Treating Co
1238 Birchwood Dr
Sunnyvale, CA 94089
(408) 736-8500
Good luck.