These can be hard to find 2nd. Hopefully you have some luck here in the Marketplace.
If not, there is a guy selling them on Gun Broker, but he wants $125 for them!!
Apex have them for $30 for the M72, but they don't have the locking pin cut out. Might be able to machine it out, if your handy with the tools. I think it would be over my head though, since I don't have a mill or a lathe. Maybe one of the members here could help you out.
Good luck with your search.