Alex is right on the demand. FR has offered a number of different Zm3 models in the past. I own a few samples and they are amazing. All are Swiss prototype. I have thought about incorporating some dual gauge action on my layout.
If you are serious about Zm, check out the Fast Tracks web site. They offer track jigs for Zm turnouts!
There has been. It absolutely did not sell. The only person I know of that produced any is Harald FREUDENREICH. It was marketed as Zm gauge. There is some available in Europe, but it is extremely difficult to find... unless you can speak and read German.
You are expecting a lot if you think there ever will be someone that mass produces any narrow gauge Z. I just don't believe there is enough of a market.
I would not be so negative about Zm. E.g. the pages by Karl-Friedrich Ahnert are in German and English, see here zm-schmalspur.de/en/
Here a Video of Zm train activity (Lahnstein 2016):
Thus, if you are in need of something specific in Zm, we are happy to assist you with that. Best, Sven