They still make these! I have one for my 1917 when I get a wild-hair to put it into "civilian clothes" along with a set of Fitz target grips.
I bought mine through eBay: Adjustable Revolver Sight - Original Wondersight for SW | eBay
If you ask me, this is a great little rear sight for an incredible price. No affiliation -- I just really appreciate something old school like this still being produced and still feeling old school.
It could easily be made with a bunch of plastic and cost $15. I'll take the steel for $50 more any day of the week.