Since you are playing as Rome, which era are you at currently? If you're still in the peninsula, you are pretty much stuck with Roman and Celtic slingers, and Celtic archers. If you have N. Africa, get Numidian archers. If you are present in the Near East or around that area, you may get anything from Cretan archers to Caucasian, Syrian, Mardian and Persian (depending on how east you go). I consider the missiles of the West laughable, but that's only because I play from the East if those are the geographic terms you'd like to use!