Hi Steve
I don't know how much sense it makes for you to try shopping for modeling stuff in Germany. The Japanese manufacturers are more expensive here than in the US or Japan. Maybe some European garage manufacturers will make sense.
When traveling to the Frankfurt area check the
http://www.museum-sinsheim.de/. Lots of stuff there and the Hockenheim Racetrack is just around the corner.
If you get as far as the Nürburgring there's a worthwhile event in two weeks
http://www.modena-trackdays.com/index.php?id=235 .....but it's during the week!
In Munich the
http://www.deutsches-museum.de/en/ has a new place since last year for cars and the likes. Haven't been there yet but it should be good. In the main Museum you also have planes and more.