I would say that the locks used by Manton would have been bought in from the lock makers of Birmingham these locks were first rough forged by the lock forgers of Darlaston ,these were then past to the Birmingham shops of the gunlock filers and then past to the fine finishers who would polish and tune in all the lock parts
Darlaston in the mid eighteen century recorded 302 gunlock filers , 60 gunlock forgers, also 250 boys employed has gunlock forgers and filers ,cock stampers and pin forgers
Feltwad
Lock makers Joseph Manton employed in his own shop:
John Asall, from 1792
John Bradford, from 1814
Walter Brown, from 1799
Palmer, lock filer, no date
Penn, lock filer, no date
Outside workers Joseph commission for work:
John Bradford, up to 1814 when Joseph employed him at his own shop.
Richard Bradney, Lockmaker
Joseph Brazier, Lockmaker
From "The Mantons" pages 191-192
Beyond these names given, there would have undoubtedly been lower rank workers who would have performed many of the more tedious tasks associated with lock making and any of the other steps in gunmaking.