Scott:

If you want to do it yourself, the Haynes manual offers a fair amt. of good info on concepts. They have a manual specifically about brake work and it's not model-specific, but conceptual in nature. These books have received a lot of bad press here, but I've learned a great deal from the "concept" books.
Pep Boys and other mass marketer auto parts stores sell them.

If you want the best rebuilt(not necessarily the cheapest), I'd call this MB dealer ship in California. I priced a set of 126 rebuilt calipers a few yrs. ago and was surprised by the price, all things considered. MB put a 2 yr. warranty on them.

This is one of those parts that I wouldn't go cheap on.

http://www.caliber.mercedescenter.com/mbcenter/b/index.jhtml