Rear sight for an IAB Sharps .50 Papercutter

[Gomezy3k]

I hope this is in the right forum, I didn't see a gunsmithing forum or any that might come close to being the one I want.   

I bought a used IAB .50 Sharps paper cutter a couple of years ago (yeah I know they are cheap) but the only problem I have had is the chamber liner moves now and then and I have to try and force it back......  Other wise it shoots great...

Anyway, the last time I was shooting, the dang rifle got bumped and it fell over and it knocked the buckhorn/ladder sight off.  I couldn't get time to try and get the broken screw out, so I put the sight where I wouldn't lose it....  I ended up moving and guess what...  Yeah, I lost it, or at least hid it so well I cannot find it... 

I need to replace the sight but need to know where I can locate one.   

Any suggestions would be appreciated...  Thanks