Hello Jörg,
please have a look at
http://www.jagdgeschwader.net/
You also can use google and look for "Jochen Prien"
or "Jagdfliegerverbände". You'll find some online shops
were you can buy this series. Or ask in your local
book shop. They can order these books too.
Ach ja, die Serie ist komplett auf Deutsch, nur ist die
Sprache dieses Forums Englisch!
Greetings to all,
Sven.