Vioworld usually has serious second-hand instruments:
http://www.vioworld-klassik.de/index.htmIf you are prepared to trawl through all of the rubbish on ebay, you sometimes find decent instruments there.
Hieber-Lindberg on Sonnenstrasse have mainly student instruments but when I went looking for flutes they also had some higher end ones which weren't on their website (http://www.hieber-lindberg.de/). Some of the sales assistents knew what they were talking about and some definately didn't.
Münchner Blech is recommended by a colleague for brass instruments:
http://www.muenchner-blech.de/I hope this helps.
Bron