I saw your posting and if you had no luck so far you should try the banks or google: Immobilien Berlin or Wohnung Berlin.
You can also try at the local Banks. Germany has a different Real Estate culture and many properties are offered and handled by the banks.
There seems to be a vacumm on international business. I can help you make this happen if you haven't found the avenue yet. As a Certified International Property Specialist (CIPS) I have access to an international network.
Email me if you are still in the market.