individual parts for compressors are not typically available IME

i usually install a used one from a reputable junkyard or "auto recycler" <img src="/forums/images/graemlins/notooth.gif" alt="" /> along with new o-rings at the junctions on the pump, car-part.com is a good way to find one

pressure wash it before you start teardown, and make sure not to get any dirt specks, liquids, etc. in the system