I'm considering on using Sarmatians for the Knights of Poitain. Sarmatians were supposedly the inspiration for King Arthur's Knights of the Round Table. So why not Poitainian Knights as well, after all they do make up most of the Aquilonian Cavalry.
Here are some decent images of Sarmatian knights.
This last image is of Scythians, but I think the would fill in nicely for infantry!
Here are some Old Glory Sarmatians. They don't have shields so I'll probably have to make some, I've heard that nail heads work decently as shields.
That's all for now. Cheers!