Fasteners to repair nuprime operator

The shoulder rivet I see in your photo would be difficult to find and install in your existing window. Your best bet might be to purchase some 3/16" pop rivets in the length you need along with some "tube" spacers to make up the diameter of the shoulder rivet to fill in the hole.

Another thought might be to use a shoulder screw like our 33-070, but I'm not sure if it would be long enough. You would also need to tap a machine thread into the one link arm of the window.