I also own a '91 vintage 92AF. It's a nice gun, and I enjoy shooting it. The white dots had faded to a light beige over time. Since the front sight is a part of the slide and the rear sights are pressed into a dovetail, I'd almost be certain that there isn't much that you can do without spending a lot of money for gunsmithing that would undoubtedly involve some machining of the slide. I have absolutely no clue as to whether it would even be feasible to adapt a different sight to the gun. In any case, you'd spend 3 or 4 times what the gun is worth by the time that it was all said and done.
I simply cleaned the sights and dabbed a spot of new white acrylic paint onto the dots with the tip of a toothpick. That brightened them up again, which was good enough for me.
