About 15 years ago I have discovered books of Christer Bergrstrom and purchased some of them: volumes 2 and 3 of "Iron Cross/Red Star" (IC/RS) and "Griff and Grislawsky". Searched for vol.1 of IC/RS but prices were exorbitant $500 or higher. Luckily managed to borrow from another guy and to read.
I liked IC/RS series but found them outdated eventually as new information about Eastern Front was made public. Recently I searched for Bergstrom online and discovered this:
http://www.bergstrombooks.elknet.pl/bc-rs/
IC/RS volume 4 will be (probably) published if the author manage to crowdfund the project.
Hope it is of interest for Bergstrom's readers and for anyone who is interested in WWII air war history.
Disclosure: I am not associated with the author/publishers.