I'm a German homebrewer, and I'm not the only one. If you speak any German, there's a forum here:
http://hobbybrauer.de/ Even without any German knowledge, there are enough of us who speak some English to help you out nonetheless.
I am not aware of physical homebrew stores, but there are several mailorder companies that should give you most of the supplies. Some things tend to be done slightly different than in the US, for example BIAB, ice chest mashing or glass carboys are rare, but there's certainly nothing stopping you from continuing your hobby in metric.