the availabilty of new or new old stock parts is no bright picture. To find these for Audi c2 one needs a lot of passion and sometimes sense of investigation. A good idea is to permanently have an eye on the typical buy-and-sell platforms in the www, but nevertheless there are almost a handful of specialized dealers mainly in Germany who take pride in their passion to help us enthusiasts.
Some Examples: Helge Matthiesen of Quickborn near Hamburg, Sütterlin of Kehl, Andreas Kuhnert of Heusenstamm and Max Pleintinger of Moeding near Landau. You will find home pages of the first three ones if you feed google search with the names and the word Audi, whereas Max has no home page but can be contacted via phone or mail. After all, even Audi Germany themselves have finally understood the need of an online-shop for classic parts, and you will find it here: http://trshop.audi.de/konakart/Welcome.do
But don't expect anything like a wide range of parts or lots of bargains as it's not a Ford Model A that were are dealing about!
Another idea to find good used parts - and sometimes even NOS - is to put a query into the "Wanted" section of this forum. Somes folks have collected a good bunch of spare parts over the years. So feel free just to ask, please!
I am sorry I cannot give further information about two tone UK models as I am not really familiar with what was offered to the UK. My interest has always been focused to US models as I have been staying in the US and CDN quite often for tours of more than 50 k miles up to now.