Have you tried Alretta Truck Parts? Back several years ago, when I rebuilt the brakes on my '52 450 I sourced the parts from there. I know the rear shoes were not available. I was able to get all the wheel cylinders and front shoes and hardware kit from him. I want to say the rear spring kit was not available, but it's worth a try.

http://www.alretta.com/


1947, 1950, & 1952 Chevrolet 1/2 ton
1952 GMC 450 series Cab Over Engine
1946 Chevrolet 2 Ton