Dennis,
Have you looked through Giles Cromwell's "The Virginia Manufactory of Arms"? He covers some of the early 19th century gunsmiths who did contract rifles to supplement those produced in Richmond at the Va Manufactory. He mentions Sheetz was the first contract in 1808 and that there were upwards of twenty men contracting rifle work and a total of 2,145 rifles produced by external contractors outside of the Va Manufactory.
Whisker's Gunsmiths of Va lists the Archers as well as Zachariah Brooks as living in Richmond (Manchester specifically) from 1793-1808 (married Margaret McRae of Powhatan Co in 1808) and in Chesterfield Co by 1821. I suspect the McRae who purchased the enterprise is likely related to Margaret.
ETA I missed his listing of the rifle contractors in the back: Sheets, Lauck, Rutherford, Higgins, Wiseman, St. John Dixon, Sites, Martin/Wallers/Strhroyer of Randolph Co, Kelly/Dixon, Laidley/Chisler, McCammant, Beirne/Honaker/Wiseman, McCammant, Beirne, Davis, Carson and Baker.
Your three Powhatan Co names are not on the contract rifle maker name list nor are they on the list of known employees at the Manufactory proper from my quick glance.