I have checked all of the places mentioned with no luck on this particilar model. This is a fairly simple sight in that the elevation is adjusted simply by loosening the eye cup and sliding it up and down. Very close to one pictured in the Madis book on the Dodge's patent rifle pictured at the beginning of the chapter on the 1866. In the chapter on sights it is pictured and just called a "graduated peep sight."
I assumed the one pictured in my above post was a repop as it was mounted on a modern Uberti Henry that is currently on GB. I guess it could be an original though, explaining why I can't find it available anywhere. Although my gut tells me it is a repro Due to some minor differences
Below are some pics of the originals. .