You need to get in contact with KCSkyrider. He's AF and stationed in Ramstein and is running meth in his 135i. I know that the shop he goes to is called SP Performance and is close to the base. They do very great work by what I have heard. Another place (but I don't know if they sell meth) is Schaefer Clubsport.
http://www.mini-clubsport.com/ This is the only guy I bring my car to when it comes to performance oriented or any kind of stuff I need done. He does work on alot of track cars and on street cars (not only mini's).
Best of luck coming over and make sure you have a set of winter specific tires because it gets very cold in this area and this last winter season was the worst in this area.