The rear sight of the same year 5.5" hb 41 looks like the same sight. A lot of Bullseye shooters took them off. Maybe try to pick up a used rear sight thru a Bullseye website.
Do you have a picture of what it looks like? - I have received a bag o parts from someone that was labeled model 52 that I have no use for - maybe it is in there.
I think some are interchangeable with the model 39 and kept em - well just to keep em. No promises but maybe a bit of luck !