It's a click adjustable sight with the little detents all around the screw head...
I'm pretty sure I would have to find another screw just like it. I think the threads in the sight itself are still there enough to hold if the screw wasn't stripped, but I'm not sure of it. My guess is the screw will be just as hard to find as the whole sight.
Numrich gun parts has a stripped slide w/rear sight for $100 but I'm not sure its the Coltmaster style. There's no picture with it so I have to wonder if its the more common Accro sight that came on later Woodsman's. I guess I could swap out the whole slide but that would be a last resort.