What you have is known as a back action lock. They are, or were, common on shotguns as well as on some rifles. They seem to be pretty scarce and I always am on the lookout for them since I like building back action lock rifles. L&R makes new ones but the quality isn't anywhere near what the older ones are. I know, I just used an L&R. I don't normally talk down products but facts are facts and you should keep looking for the older ones.
