Hello,
I am not talking about the standard V-notch rear sight, but the V-notch rear sight offered on the Old Armory Original. Take a look at the Old Armory Original page on USFA's site, the rear sight is different than the standard V-notch offered on USFA blackpowder frame guns. There is a trench that tapers into the V-notch. I found a picture of an original SAA built in 1881, and it indeed has this rear sight, just like the Old Armory Original.
USFA's website seems to indicate that this is exclusive to the Old Armory Original series revolvers. I have been unable to find much of anything about the Old Armory guns, it would seem that they are not big sellers.
Jared