I bought a replacement aperture rear sight for my Ruger Mk 1 some years ago and frankly this thing as done more for my accuracy than anything except Billlls Pistol Stabilization Fluid*. People have asked me about it and I send them off searching for the maker, oneraggedhole, who at this point seems to be not only out of business, but also deceased.
What I'm finding is that when he died, he was supplying these sights to a couple of retailers as well as selling them himself and his survivors apparently unsuccessfully tried to carry on. The sights are now unavailable anywhere and the website is "available" from someone.
The sight was a very simple piece, a slip-in flat piece of metal with an aperture hole in it, either 7/64 or 9/64" diameter. Rear sight attachments being very much unique to each brand, this item didn't fit everywhere but was available for brands that allowed the flat part to either slip in or screw on. A quick patent search revealed nothing although my experience is that patent trolls are a clever lot and the inventor's family may even have the patent under some obscure filing name. The originals were made from very soft steel which would bend if the gun was stored in a soft case upside down. They would be very easy to make in mass quantities from better steel if there were any interest.
Anyone have any more information?
* Decaffinated coffee.