They have a museum shop at the old VW museum and at Autostadt.
There also is a shop called vw/audi classic parts, and they sell parts that are not in production now. NOS parts for the most, and some repro. If you search on
http://www.volkswagen.de you can find out more there!
Don`t forget that if you are in Europe in june, the biggest VW event in scandinavia is in Sweden 10-12 June.
http://www.bugrun.com