I'm doing the same thing myself, and have had good luck with Jireh and J&P Cyles. Their catalogs are free for the asking and between the two I have been able to find all the parts I need.
Or you could try your local shop. Most small shops are being run out of business by places like Jireh. The local shops are a lot more help than some computer place selling parts. Is there any tech support from Jireh?