Why half-size? A full-size 12-pounder Napoleon will fit in the back of a pickup as easily as a half-scale model. And if you don't have a horse team, a 4-wheel ATV will do for local movement.
Either Paulson Brothers, Steen Cannons, or South Bend Replicas can fix you up, either way, full-size or scale. But you will NOT be paying half the price of a full-sized gun for a halfsized replica, and if you can manage to get the one, you might as well go for the whole hog. Or as far as that goes, the sleeved-barrel 6-pounder available from South Bend is a fine little piece.
And if you do happen to choose to do business with Paul Barnett at South Bend, tell him archy sent ya!
I've tried to sell the decorative aspect to my family, the half size fits better. Plus I've no where heated to store a big one year round. Thanks for the links.