Rockauto.com has a "wholesaler clearance" on some Vanagon rear wheel
brake cylinders. Search for p/n 78494201. Last I saw, there were 10
left, at less than $3 each. I got a pair while ordering some other
stuff, just to see what they were, and was pleasantly surprised. They
have springs in them! I installed them, they work fine. Ordered a
lifetime supply for myself, cheaper than even rebuild kits.

They're a bit different than the OEM ones, instead of a ring type seal
which is installed on the pistons, they have separate cup seals. The
springs hold the seals against the pistons, in addition to holding the
pistons against the shoes.

This is an age-old design which is well proven. I actually prefer it,
there's only one place they have to seal - against the cylinder wall.
The OEM design also has to seal against the piston.

One thing to watch for, this type is a bit more fussy to install, if you
push the pistons in too much when installing them, the cups can get
cocked and leak. No problem once they're in and bled.