What kind of car? I own an Audi and the audifans.com site has been really helpful. There's a couple of good junkyards in Denver one of which specializes in Audi parts and Slipstream automotive does a bunch of high end work. My '87 wagon is chipped, with upgraded suspension, brakes and turbo. It's damn fast and the other day I easily dropped a guy in a brand spanking new Audi 2.8 turbo Allroad going up the hill west on I-70 out of Morrisson. It totally pissed him off and a couple miles later when I slowed down he passed me going about 100, just to prove he could go fast, too.
Of course, you probably have a Neon or something! haha, just kidding. The web will be your best source for high performance stuff and there are plenty of tuners in the area that can hook you up with info