When I lived there in 1978 there was quite a good one, just south of Templehof Airport on the west side of the highway. He had lots of plastic kits as well as some R/C gear and larger size boat kits and stuff too.
I checked on Google Earth and it looks like he's moved, but not far away.
It's Kehrer Modellbau
Peter-Strasser-Weg 18,
12101
Berlin,