Randy Johnson's California Mustangs still making these? If no, are their other non-altenator 12v options?

Sure, just change all the light bulbs and install a 12 volt battery. The generator won't know the difference.

If you are using a modern voltage regulator it will need to be changed to a 12 volt version.

The battery cable from the battery to the starter needs to be changed to a 2 gage, at least 12 feet long. This will limit current from the 12 volt battery to the starter.

I could care less what voltage you want to run your T on, but after all the tinkering around to make stuff work correctly and last long, I found just doing it the way Henry did was the best. Just my honest opinion after messing with this stuff on both 6V and 12V.

For me, I had to change some things back, that if I had just done it on 6v the first time, I would have came out ahead dollar wise.

But as Royce says, you can just change the bulbs and run a 12v Fun Projects regulator on it and be on your way. The extra long battery cable to get a ok voltage drop to the starter, to me is a nuisance. Again, my opinion.

That is all fine if you are so disposed, BUT it is important to remember the original Model T generator only has the capability to reliably produce 100 Watts of power.
Simply that means you CANNOT set the generator charging rate over 7 Amps when charging a 12 volt battery or you exceed it's capability. If you do, the generator will not last long and a fully rebuilt generator (not a patch-up) costs around $400.
Ron the Coilman

To answer Contantine's question, Yes he is still in business. See contact info on suppliers page. I have run one of his generators for over 30 years and and another for over 20. Never had a failure.

I have run a few of these 12V generators, they are adapted from later Ford generators. I have found that they are reliable, but do not work well at the lower RPM range of a model T, and more complicated as well. I like to use the model T generator with a Fun Projects regulator. It gives you 12 volt charging and looks original. Be sure to pay attention to Ron's post above as well as the instructions for the regulator. Do not overwork the generator or it will fail.