There is no tang, so no one makes a "tang" mountable sight, Marbles does make the #009813 that would work on any H&R, but drilling and tapping would be required as well as mounting to the stock without the addition of a false tang. There are bolt on barrel mounted sights available that use the existing scope mounting holes, those are shown in the FAQs and Help sticky, see Peep and Firesights and Long Range Sights.
Tim