OK, we know that Track used to carry these, some time ago. They haven't for a few years, at least.
The last time I was at Friendship, I talked with a fellow named Michael Lea and he said that he was making them also. Now that's been quite some time ago, but I would imagine if he is still kicking, he could still do it, if he was so inclined. Of course, that was back in 1992, so things could have certainly changed. The business is called Michael Lea and Daughter, Columbus, OH. I see he teaches an engraving class at the Log Cabin Shop which occurred as late as 2019.So, I would guess he is still a viable source.
While we are talking about things kinda like that, what I have long felt a need for is an Irish Shot Valve and an English Shot Valve that is American made and priced a bit more reasonably than the ones from Pedersoli. Just a thought.
John (Bigsmoke)