Blau,

The US RS6 didn't come with front parking sensors.
However, I did test drive one in 2008 in San Diego, CA that was a lemon law return that did have front sensors and rear sensors. There wasn't a button in the dashboard but I clearly remember it chirping as I got close to the curb.

I have also read on here that there are several "unicorns" that were exec cars with front sensors.

It would seem that it would be an easy retrofit as ETKA has diagrams for it and part numbers.
As far as the dashboard module, suggest ebay.de...