Muskaleitis

Hello everyone! Me and my subaru just moved to UK, and I know almost nothing about where to buy parts, what is the best way to get them e.t.c. So, could you guys, give me some guidelines with cheap websites where to order parts by part numbers? (I check them at opposedforces.com) for example, now I'm looking for exedy clutch. Oh, and I own subaru legacy sedan, 2.5l, 2001.