Brownells is the answer in the long term Sweettooth.
I would only buy one if I were you, BUT, you need to know the size.
Look at other guns at the match today and ask questions. Ask if anyone there has had to order and see what happens.
There is always a chance that someone at the match will have one they might let you have.
Short term, see if you can find a small bead around the house (or some small round object) and try to apply with super glue.
Hope this helps.