I think the Conquest Sauk & Fox Indians could also be pressed into service as Seminoles with only minor modifications - a little green stuff to modify the haircuts, add turbans, plus adding a little fringing to the long shirts. Although the available minis always show the Seminoles looking pretty resplendently dressed, there are actually plenty of reports of them fighting nearly naked or just wearing a breechclout.
Another possible addition, although it initially sounds a little unlikely, are the Maroons from the Foundry pirate range (see for instance CUT3/4). Escaped slaves were an important issue in the various Seminole wars, and there's an illustration in the Osprey book showing a maroon with the Seminoles that's a dead-ringer for the Foundry stuff. Over time, the escaped slaves joined with the Indians to become the Black Seminoles (of course, Conquest do Black Seminoles too). Freed slaves and Indians joining up to fight - a bit of an American colonialist nightmare!
Finally, while I'm riffing on the subject, I don't imagine that you'd actually need all that many Seminoles to make a good game anyway - half the fun of the period would be using the swampy terrain almost as a protagonist. Plenty of fun with soldiers dropping down from the heat and fever, getting lost, bitten by alligators etc.
It's a fascinating period - the Second Seminole war was the longest and most expensive Indian war the US army fought, and was very controversial on the home front. Add in the local Florida terrain and you've basically got Vietnam with Indians! But it ran alongside events at the Alamo, so it often gets rather overlooked.
Damn, I think I jut talked myself into starting a new project...