Typ 89 rear calipers - a source for new?

[radek at istar.ca]

Hello group.

The rear caliper in my 88 90Q is leaking again through the handbrake shaft.  It's the
early version, I 
think it's 35 mm in diameter.  Since I have already dismantled it and cleaned three times
within the last 
year, I'm about to give up and buy a new one.
However, factory-new calipers are not available here in Canada.  So here are my questions:
1. are brand-new rear calipers available in the US?
2. can calipers from later models (larger diameter) be used - in pairs of course?
3. any good source for rebuilt calipers (the guys here basically just repaint old ones and
sell them 
as "remanufactured", I don't want that.  If I buy a remanufactured caliper, I need all
rubber, including 
the o-ring that seals the handbrake shaft, to be changed).
4. I tried this before, but has anyone a source for those o-rings?

Thanks.

Radek 
88 90Q
91 V8Q 5-sp.