Depends on whether you want second hand or new? Nengun have new products (and second hand) and seem to cheaper than other suppliers. I've got most of my parts from nengun and never had a problem.
Greenline are sometimes cheaper than Nengun on some parts.
Depending on how mechanically minded you are I guess is to whether you pay someone to do it, or do it yourself. Adrian (strutto) has a fair bit of knowledge about the SAFC's, I'm sure he'd give you some information if you required it.
Tuners around the place. Theres the usual Autotech, Mercury Motorsport. Not sure about Matty Spry (I know he does PFC's, I gather he'd do other plug in parts).