Hi Colin
I'll Start with a question, which truck are you looking for the booster for?
Reason I ask is that the system seem to be such a mix and match of Chevy and Ford parts used on the same trucks.
Now the pictures below are the brake booster that is found on my Pat 12 C60L and Pat 13 C60S.
Bob and I found some NOS units a few years ago at
http://vehiclesofvictory.com/ but I think we got the last two, they went cheap because they did even know what they fitted. I just tried to check their parts list and could not see any more listed.
Hope the images help.
Cheers Phil