Welcome to the forum Nick, you'll find the members on here are a friendly and helpful bunch :)
I'd say look on eBay first as this will give you a good idea of specs and colour combos etc. Then I'd look at specific Audi, VAG or german car specialists.
I wouldn't always direct members to other forums/clubs but there are dedicated TT clubs which will.be a good place to look as an enthusiast owned car is often more well looked after.
Hope I've helped.
Cheers
Steve