Good luck in your search, I too am looking for prechambers.
I resorted to knocking some out of another head I had, the problem with this is they are larger so I have to have a machine shop CNC the holes for the new ones. They are charging me $100.00 to do it.
I have asked them to hold off for a bit so I can look for direct replacements.
I did a search here and on other sites and came up with a few links but non panned out.
dan