Their special field is GDR. Further assembly areas are old Germany, SBZ and federation.
http://www.deutscher-philatelie-service.de/

Albany Stamp Company, Personal Service for the beginner to advanced collector. Specializing in French colonies, Asia World wide Topicals, and Holograms.
http://www.wmwtech.com/cgi-local/shopasc.pl/page=index2.html