I already have some 6mm figures coming my way from Pico Armor (http://www.picoarmor.com/pages/home.php) for my Thunderbolt Apache Leader. These would be perfectly suited for the conventional forces, and Pico has a line of 6mm WWII that would also fit the Reich forces.
Items such as the Haunebu, Scourges etc will be more difficult to find however, but it would be interesting to know if something along those lines exist.