Hastings Slug Barrel Sights

Need some help.  Looking for a rear sight for a Hastings Rifled Slug Barrel.  The model that I have is a "paradox" and is for a Rem 870.  I contacted Hastings and they could not help as they stated they only have sights for their current production barrels, which is different from the paradox design.  I have the base and the dovetail mount but not the adjustable part for the rear sight.  Any recommendations?

Thanks for the advice.  Will contact them and see what they have.  I also contacted Williams Gun Sight over in Michigan.  They were checking on availability also.  Hastings told me the company that made the sight for this model has gone out of business.

Brownells  or Old West Scrounger  maybe  ?