A warning to anyone trying to file down swivels, does not seem to work. The swivel on the right breached the inside before I got anywhere close to getting it to fit. The swivel on the left (from the handstop) got pretty close but as you can see by the small circle forming in the center I was about to also breach the inside.
Back to option 1 - Find somewhere to buy the swivel. Looks like WGC shop has one
here. Unfortunately you cant see the back of the swivel but its my best idea at the moment.