hy there,
I've worked on different porsche's over a couple of years know and I buy my spare parts most of the time from FVD. Most of the time their prices are reasonable. They don't have everything but maybe they can help you. You can also check other porsche type's than the 944. Porsche often used the same calipers on different models f.e. the 928 S4 has the same calipers as the 944 turbo S. (Make shure to check the piston diameter). Here is their site
http://www.fvd.de/
Friendly regards,
Tom
Ps: I have no experiance with their online service because I buy my parts from a local distributor in belgium.