What sort of aftermarket clutch? like a sachs sport clutch, an M3 clutch, etc.
What is the current issue with your stock clutch (aside from slipping if it's worn)?
As for getting a clutch, there are plently of places, your best bet though would be to take advantage of the low US dollar and ship something in from the states.
"Driving is like a narcotic, an addiction that can take over lives. It ruins people, breaks families apart, and even kills. Itís habit that needs to be fueled. Time, money, rationality, sweat, knuckle skin, and anyone who disapproves are of little importance to a driver, and are often overlooked. Hi, Iím Nelson, and Iím a drivaholic."