Phil I saw this thread which has those star caps you are asking around about. http://www.audi-sport.net/vb/showthr...719-RS6-Alloys. At the time of posting the quote was 15 quid a cap.
On ebay USA the part code is 4F0 601 165
http://cgi.ebay.com/ebaymotors/AUDI-...item3eff50c4ac. Not sure if this is the correct part code though but maybe helpful to your quest!