These have been out of service for so long now. I doubt that pretty much any spares are available these days!
I would suggest, you look for an unserviceable one. IE: The bodies on these sights were made from an Alloy. & it was common for them to fracture where the front long thin section(Where the adjusting screw & retaining catch assembly are mounted tapers towards the thicker main part of the Body.
A Fractured sight unit is pretty well useless for anything, other than breaking for spares!
You could then canibalise one for what you may need.