Like Fumblin46 I check eBay on a regular basis and often bid on parts even if I don't need them at the time. I also check with several vendors to get best total pricing (be sure to figure in shipping).
I am currently rebuilding the brakes on my 53 3/4 ton. I bought parts from Chevy Duty, American Classic, and Jim Carter's. All have good service. Since I place most of the orders on the web, I can't comment on their telephone order staff.