http://www.carbonrev.com/product/audi/P1
Buy two of the R8 front sets and you should be good to go. You would be into 19s for less weight than light 18s. Granted you will pay through the nose. I believe these are the same wheels as the Mustang GT 350R.
Nene, as purveyor of pricey (nice) wheels, these sound up your alley.