they were made from 1974-1989
mounting a scope and not damaging the pistol---------there could be a way but you would have to make the mount and use the rear sight holes
now I did find a dovetail mounting blank on Ebay from China that I had been working up a mount for the model 5's and 6's
the lucky part was the factory sight was the same width as the blank, so placing the holes was easy but you have to relieve the back side and find the right screws so they don't go past the inside of the tube
I have a spare tube so that was easy
now the blanks are let say a bit rough but with enough elbow grease you can make them look ok and so myou can reblue them, in the model 10 flat black
they are not a perfect match on radius but close enough to work and with some weaver adapters they will work, a project 3/4 finished
to my knowledge there was no mount made by the factory
https://www.ebay.com/itm/Steel-11mm-Round-Bottom-Dovetail-Rail-Base-For-Airgun-Rifle-Laser-Sight-Scope/252885659997 now if pistol is shoot fine now and you have no history on the pistol look at the 2 side cap set screws and the rear cap screw and see if there is any sign of being removed, also how is the breech seal O-ring
if so, it has been more then likely been resealed and you should be in good shape, if it has original seal in it, they will fail very soon and I said seal because I have never seen the rear piston seal that was in bad shape where as the front seal will be a crumbly mess
just some info and maybe an idea, I'm a owner of many Giss System pistols