I'm sure there are aftermarket sights that will fit on it. Take the barrel to a local gun shop so that they can match the hole spacing of the mounting screws. Most shops should have an assortment of sights in stock and if they don't, it can be ordered. I don't know the center to center measurement and can not give you a specific one to go on it. The fibre optic sights are the best to use and the Williams may fit it.
You may need to have an extra hole drilled and tapped to mount a new base. There is a huge selection of styles available.
Another suggestion and the best way to go is to put a scope base on the receiver and use a Reflex sight. The Saddle mounts go on by sliding over the top of the receiver and replacing the trigger guard pins. There is no gunsmithing involved.
The Browning reflex sight has 4 different reticles. Just put the dot or cross hairs on the target and shoot.
I hope this helps you,