I've had the pool ball for a really long time and don't really remember how I got it. I'm sure you can find some on ebay or amazon. Here are the clasps I used.
edit: and thank you!
I'll add a suggestion here, too. If you're doing anything where the rope is providing tension to a structural element, or if you're working in chains or straps or something you can't cut, get a set of panic snaps with a swivel eye.
They let you quickly & safely disconnect your subject from the rigging so you can reach any part of the tie.