@Mr Martyn, I am assuming you may have some of the standard "arm chair historian's" reference works, since you only asked about figure manufacturers? I no longer game "1812," and when I did it was in 15mm. However, I use Old Glory 28mm F&IW/SYW figures and like 'em well enough, but I do understand that for some folks OG figures are not to their "taste." Still, I'd think about it…
@michaelsbagley and others, as you ask about Northern & Southern and uniform variations, I'd humbly suggest picking up, if nothing else, the relevant Osprey's if you think you might do "1812." And assuming you don't already have 'em!!! 
The US regulars from Old Glory should be just as valid in the southern theatre as they are for the north…
As already noted a long time ago in another galaxy I did "1812" in 15mm, and, was a subscriber (now sadly lapsed) to the pubs of the Company of Military Historians; somewhere I have most of my plate collection, although a basement flood ruined a few.
You're going to have to be pretty "aggressive" to want to drill down on the minute differences in American uniforms between what "I" would call the "North-western," the "Northern," the "Eastern" and "Southern" TsOW. I.E., the Niagara, Champlain Valley, "Coastal," and Gulf Theaters (Gulf encompassing the backwoods of the "Old Southwest" and Jackson's campaign against the Indians there). By "drill down" I mean: when did the order go out from Washington to adopt new clothing, when did the commands receive and acknowledge same, and MORE importantly, the Depots/Magazines (and principally, Philadelphia Arsenal), and when did the commands receive new clothing?
If you've got Xerox copies out of the unit Letter Books to show that, say, Brig. Gen. Jethro Tull's brigade only received enough of the new "1813" uniform to cloth the US 79th Infantry on 14 March 1814, issued it to the eight companies of the regiment present at Fort Lost-in-the-Woods on 15-25 March, and the brigade then marched out with the US 65th and 69th still clothed in the now-shabby "mixed" uniforms they had received in the winter of 1812/13 to do battle at Puddler's Pond on 5 April, then I say, "drive on!" [I jest, there was no US 65th, 69th, or 79th.]
The Regulations of 1810 (see US Army Center of Military History) called for the Army's "Winter Uniform" to be a blue "coatee," with red collar and cuff. The pre-1810 red facings (lapels, if you will) were eliminated, and the coatee front closure was held together by hooks and eyes, its two rows of non-functioning buttons surrounded with white lace binding. The pre-1810 soldier's "Round Hat" was replaced with a flat-topped shako, aka "Yeoman Crown Shako." Most officers wore a long-tailed version of the coat with either a bicorne or shako, though "company officers" might wear a better version of the soldiers' coatee, and the more affluent effected hussar-style boots instead of "shoes."
Blue cloth being hard to come by after 1804, as it was mostly imported from Europe, alternatives were resorted to in 1812 clothing all but the "old corps." For the winter of 1812/13 at least, the first seven infantry regiments wore the prescribed uniform. However, according to the CMH, "Beginning around 1800, white linen roundabouts were issued to troops south of the Potomac River for summer wear. Issue was extended to troops in northern districts during the War of 1812." These "roundabouts" or "summer uniform" are what folks often mean (as I discovered when pressing opponents when I war-gamed in 15mm) by the "Southern Theater" uniform. The coatee and trousers were cut in exactly the style of the then-current "winter uniform," but were of completely unadorned white or off-white linen, and the coatee was secured by a nine-button front.
As the CMH notes, the linen uniform could be and was issued in the "North" from 1812 on-wards -- as a stop-gap when new regiments were raised in the war, or in summer if the old winter gear was worn out. This bought the Philadelphia Arsenal and the Commissaries five or six months time to try to get new "proper" winter uniforms. To add to the Federal troops' difficulties, the states sometimes had the cash to out-bid the central government contractors for the supply of available blue cloth to clothe their militias!!
JUST to confuse things further, in a cost-cutting move just before the war broke out, NEW Army Regulations were issued in February 1812 calling for a single breasted "coatee" with red collar and cuffs, but with the double-row of false buttons with the hook-and-eye closure system replaced by a cheaper single-row, 10-button front closure, with white "binding lace" for infantry and yellow for artillery (white or yellow metal buttons respectively). That explains why the "old corps" needed new uniforms in 1812 when the war started, as otherwise they should have only needed a LIMITED re-supply to replace worn out articles, since without the requirement to clothe the men in yet another a new uniform style in just two years, many men probably could have been able to keep wearing the uniform of 1810/11… albeit maybe with some repairs…
So, to the "new regiments" of 1812 in the winter of 1812/13. Many if not most of them had a uniform CUT properly to the Feb. 1812 Regulations, but varied principally though not exclusively in the color of the coat:
12th: "drab"
15th: "mixed" (i.e. mixing of the wool thread resulting in a kind of grey)
16th: black
17th: a mix of black, blue, brown, and drab coats -- I have no idea if an attempt was made to at least put each company in the same color.
25th: blue coatee; red cuffs & collar (but the white binding lace on the collar only).
26th: ditto
27th: ditto
28th: ditto
In addition, if I read the source correctly, some of the 17th's brown coatees came with GREEN facings, not red, and some musicians (in all these units?) got green coatees not red (red was specified -- i.e. the old "reverse colors" for the music).
The financial burden of the war being what it was, yet more regulations changes came quickly. In February 1813, the white binding was ordered eliminated. The CMH then states: "In May 1813 uniform regulations were again revised. The new uniform coatee was to single breasted with a 10-button closure in front. The red collar and cuffs were eliminated and lace binding was to be on the collar only in either white for infantry or yellow for artillery. The regulations also introduced a new cap or shako copied directly from the Belgic-type cap [or "tombstone"] worn by the British Infantry."
The Rifle Regiment wore a similar 1812 winter uniform to the infantry in "bottle green," and green hunting shirts in the summer. When three new Rifle Regiments (#s 2-4) were added in 1814, they were clothed in grey of the 1813 pattern, with the "tombstone" shacko. It is speculated the old regiment (by then numbered as the the 1st) managed to keep its green winter uniforms, but took up the new shacko.
Ref.: Years of Growth 1796 – 1851. Military Uniforms in America, Volume II, edited by John R. Elting (Warwick, RI: The Company of Military Historians, 1977)
