Best place for parts?

My car has had a front end knock sinse I got it 6 months ago and I think its gradually getting worse. Every garage I take it to can't find anything wrong so I'm going to start changing things myself. I had a MK4 golf that did a similar thing and it turned out to be the arb bushes (again, no garage could find it, I worked it out myself!) so I'm going to replace those and I was also planning on replacing the suspension top mounts too as they seem to crop up on here as a problem part every so often too.

So where does everyone go for these parts? Is there a decent place that will stock them or is it an Audi job?

Cheers in advance.