Another hardware question

Maybe not as titillating as sex bolts, but since we're talking hardware,
does anyone here know the correct name for, and, hopefully, a source
for, the little expansion spring bands fitted to rivet squeezer dies to
retain them in the yoke?

I've googled endless search terms including various combinations of the
words "spring," "band," "collar," "expansion," "tolerance," "ring,"
"retention," etc. etc. and come up empty-handed. The aircraft tool
distributors with whom I've spoken haven't been able to help, either.

I know they're not unique to this industry. Various machinists and
engineers with whom I've spoken locally have seen those things before,
but somehow can't quite remember where or when or what they're called.

I think if I had a real name, I could find them, but maybe even that
won't help.

I know there are tricks to keeping a die in place when the band is
missing, but I'm not looking for a band-aid. I'd like to manufacture a
new type of die, and so I need a fair quantity of those things.

My undying gratitude and the first production set of dies goes to
whomever can help.

TIA
Jon