Reference Books Source?

Anybody know of any cheap reference books please on the Post War DDR Military up to early 90s?

Have loads of the Osprey/Men At Arms books on various other subjects and while not the best can be picked up cheap second hand.

Thanks

Osprey should do one on the East German military. I've hit their site suggestion box many wonderful times with that idea. The warsaw pact armies is waay out of date. Much of what I use for reference comes from copies of "Armeerundschau", the "Handbuch Militarische Grundwissen", and the like I've picked up off ebay. The Thomas M. Foster "The East German Army" can still be found on Amazon etc. IIRC the last edition was published in 1984.

I thought Osprey did a good job with their Fortress book on the Inner-German border.