There are about a page and a half of "Green's" in Blackmore's Gunmakers of London about half of which could be your man... and that is just presuming the lock came from a London gun. It could be a provincial maker and practically nothing is known about those. There is ongoing work on specific localities... Oxford, Bristol etc... but the bulk of the provincial market remains a huge unknown, especially in the mid-18th century and earlier because they pre-date city and town directories. Without the rest of the gun, I'd say its @!*% near impossible to get much closer than the mid-18th century... England. Even with the rest of the original gun, it might be difficult to nail down a specific maker.
At least you do have a recognizable signature on the lock. Your best bet would to identify a complete gun with a near identical lock signature that can be attributed to a known maker.
