Hmmm, looks like 1 3/8" is the smallest they make, far too big I'm afraid.
I've looked at so many things, amish washers, cupped washers, ribbed washers, paper tube ends, cylinder ends, bottle caps and on and on.
What I basically want is a simple flat washer with a shallow ridge on the outer perimeter about the same height or slightly higher than the atty connector will be when set into the center. It could be anywhere from a half inch to an inch and probably work, but ideally the outer perimeter would allow a 23 mm RBA to sit inside of. If not, then I would have to use the o-ring system you showed previously.
Sourcing parts is one of the hardest things I have to do, takes forever and I've been looking for alternate catch cups for years. I might just have to make my own on the CNC machine with delrin sheets or something... arrggg