This is a short list of some of the most reliable vendors. We also recommend using e-bay, but only bid on an item after checking with the unit authenticity officer.
 

Great Source for field gear and Camo..
Great Source for Uniforms, Ed Walton is a wealth of knowledge and will get it right the first time.
source of repro low boots (look under Luftwaffe foot wear), great camo.
Another good source of field gear and the occasional trinket
Good Blanks for K-98 are hard to come by, weve never had a problem with Duffys
Great source for field gear, uniforms, and lots of little stuff as well
This guy has it all and gives us great deals. Our one stop shopping source! Eric and his wife are the best to deal with.
Great Tunics and absolutely the best to deal with. Our choice for custom and larger tunics.