I have the same kind of rear cylinders on my truck that you're describing and I know that Car Quest sells the re-build kits for them, but I'm not sure whether they sell the entire wheel cylinder itself. It might be worth a shot, though. If you're looking for the 1-1/2" diameter original-style slave cylinders, Napa carries them. The only downside is they're about 90 dollars apiece, but it's an alternative if you can't find the ones you described.
