If you go to Weaver Optics' website, you can search under "Mounts".
They don't list the 86C, but they do the 87, which is apparently quite similar, even though the 87 is an autoloader. My Dad had an 87 with a Weaver Detachable Side Mount. ( I bet the receivers are the same outside diameter, etc.)
Weaver still sells the Detachable Side Mount base, but the website doesn't show any compatible rings.
The rings were (permanently?, I don't recall the exact arrangement), attached to a special sub-base, which fastened to the Detachable Side Mount using a single, large knurled thumbscrew. The Detachable Side Mount Base was on the left side of the receiver, and the sub-base kind of angled off at 10 or 11- o-clock, but the scope ended up topside , though it may not have been perfectly centered over the bore.
Hope that helps.
If you can't find parts new, I'll bet any older gunsmith has an old box full of them on a shelf somewhere.