Proportioning Valve availability??

[Huck]

My brakes suck and the best guess is the proportioning valve is shot. I tried resetting it with the little pin at the end but ----it doesn't appear to exist. I know I can buy one of these valves from parts dealers for around $90. which is way too high for what it is. Anyone have a source for new or rebuilt valves at a reasonable price? I don't want a used one as I've tried that route.
It's for a 72 truck/blazer. Any help will be greatly appreciated---Huck