Georg,
Thanks for posting photos. Lucky man having two C3/M82s!
The scope rings are much easier to find than the scopes. I think some ZF69 had 1 inch diameter tubes and some had 26mm tubes. For a 1 inch diameter scope tube you will need PH RALS3 rings (L= low, 3= 1 inch) and for a 26mm you will need PH RALS 4 (4 = 26mm).
My M82 has a ZF69 with RALS3 rings. If you find a correct scope without the rings let me know as I have a few spare sets.
Did the top rifle come with it's safety catch fitted as I when I saw it listed for sale it looked like it was missing?