I bought a Smith wesson piston model 39-2 and the old owner put a rear sight who don't fit, all is shaking and i know it's not the good sight. I wrote to the company Smith & Wesson and they told me than the rear sight for a model 39-2 is discontinued.....Is there someboy who knows what kind of rear sight than i can put on it? I want to shoot distinguish match with it so i need an ajustable rear sight,tahmk you