I know you said south......but I second the idea of a pilgrimage up north. You can come home with other standard capacity things to make it worth while.
I think Anglers Sport Center in Annapolis used to sell it but they may have stopped. It might be worth giving them a call.
(410) 757-3442
All the skirmishers buy in bulk from Back Creek Guns, right outside the Fort Shenandoah range, near Winchester, Virginia.
That's where I get my powder, and from the Baltimore area it's closer than I am. Otherwise, I'd ask how much the OP needed.Here's the link. Looks like he no longer sells the five pound bags, but you can get a 25 pound case...
Notice he says to call first and make an appointment.
http://www.blackpowderva.com/
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Give the Gun Shack in Mt Airy a call, they used to carry it years ago.