Also, I was amused that the recent article here on the "tiny emulators" (browser based) featured both KC85 and Robotron Z1013 emulators https://floooh.github.io/tiny8bit/ -- I imagine the author must have some GDR connection as those are pretty obscure elsewhere.
http://www.robotrontechnik.de/html/forum/thwb/index.php, I think you need to ask for access though.
You can check out some of the games running in emulators here:
https://www.lanale.de/kc85_emu/KC85_Emu.html
...and in my own emulators here (not as complete as the above link though):
https://floooh.github.io/tiny8bit/
Oh, and there's also:
http://www.kc85emu.de/ and http://www.mpm-kc85.de/ with lots of scans of old manuals, also information and photos of the hardware.