I don't see any Illyrian cavalry in the Baueda Roman range. I think the Illyrians were under heavy Celtic influence, so you might consider Gallic cavalry. Otherwise, I might consider using Thracian, Italian, Greek, or even Iberian cavalry.
The Xyston Thracian are really nice, but I am not sure of size differences - since some of their figures got really big for a period of time. I believe the Cappadcians are quite large; Thracian, Greek, and Romans smaller. Not sure a out Gauls and Italiotes.