I had this problem in the last version as well, seems there no where you can build a Axillary barracks to get creten archers
Iv built one in Sparta because the help tool lists it as a place to get them, and in the last game I tried recruiting them in Syracuse across the water and I had no luck there ether seems like you just can't get them
Im not talking about the mercenary ones but the Axillary version mercenary creten archers are pretty useless because you just recruit enough of them to be worth it.