Here's an interesting thread from a few years back about arms captured at Mount Vernon --
http://history-sites.com/cgi-bin/bbs53x/alcwmb/arch_config.pl?noframes;read=8977

Fuller and Stewart, Firearms of the Confederacy, opens with a chapter on arms captured at different U S arsenals. Mount Vernon received a shipment from the Springfield arsenal of 9,280 M1842 Harpers Ferry percussion muskets. The shipment of Dec 29, 1859, also included 5,720 altered SB muskets, models 1817 and 1840. Mount Vernon had already received 2,364 of the latter a month earlier.

Note that both these huge increases to arsenal inventory took place immediately following the Harpers Ferry attack. Other Southern arsenals were receiving similar shipments.

The "George Law" muskets were included in Col Powell's purchases in New England during Nov-Dec 1860. These would have been stored in the Alabama state arsenal at Montgomery AL. The state senate journal includes an interesting trial of muskets from the state armory. Total arms purchased appears in the other post. Powell had difficulty finding good arms because he had to compete with agents from other Southern states, and agents of Victor Emmanuel in Italy had nearly cleaned out New England before he arrived.