Long time ago, back in the 1980s, Frontier Miniatures (remember the Modeller's Mart catalog?) produced one (1) mounted Seminole figure. He was dressed as an early 19th century Creek, in a long fringed hunting shirt and a turban with plumes, musket in his hand. It was a true 25mm figure, and nowhere near current sculpting standards. Impossible to find these days.
Good luck with your search, I'll be interested to know what else turns up. And thanx for that pic of the Perry figures, Marco.