Yeah, it's irritating they went from easy to get to just gone! When I called PetroRelics, the guy there told me about how you just cant get them now. They stopped making them around start of COVID I think.
You may want to try some of the facebook groups, I'm in "Neon Clocks" and "Vintage Neon Clock Collectors", fair amount of buying and selling of clock parts in there. Not cheap in there though.
There's still a few on amazon too. I think it was Hansen that was the last company that was making them. So I think you can search for Hansen, Synchron, etc. If you click on "buying options" there are still a few floating around.
LINK HERE--->amazozn link