Your chances of buying a factory rifle part from Soviet Russia era are zero. They invaded Ukraine and no one wants to be their friend anymore.
Instead, you should figure out the sight base dimensions, and make one with a file. Yes, it is going to be a lot of effort, and you'll probably miss watching the playoffs. But, firearms are little machines. They are made by guys in shop aprons with benches of hand tools. Some have more handiwork than others, but all were touched by workers hands. This is your chance to be part of the continuum.