I think just about any 3/8 inch sight could be fitted to the old dovetail for the rear sight.
Lots of them available for around $20.
I like the marbles bullseye sights.
http://gunwatch.blogspot.com/2015/12/review-of-marble-arms-bullseye-sight.html
Thanks. Someday when I have more money than sense I’d love to have this old thing restored. I got it at a garage sale for $5.00.
L