I had a BMW with a Bosal hitch, nice quality. After visiting their page, click on products, then hitches to see an example (generic shown) http://www.bosal.com/BIM/index.html

Here's a retailer's page for several brands:

http://www.kupplung.de/

Do a search for Anhänger or Anhängerkupplungen or AHK.

MarkC