Is it rear? Well I usually put the crank in front.. Okay seriously, I don't think they are impossible to find but they ' trade ' at this price often enough so is reasonably priced, yes.
Consider the labor which goes into creating one of these and the skill, especially with 1970's or 1980's technology.
One could certainly make these today, water-jet-cut / laser-etch etc. You would need a chainring to start with and probably a bit more money than this is priced at.
Here is an unknown imprint on a Campy chainring for sale on ebay as reference:
https://www.ebay.com/itm/Vintage-Cam...EAAOSw6DtYSK9l
PS. N.O.S Regina Chain w/hollow pins and Olmo bar-tape are spoken for ..