Wild Camels, Llamas and Snow Leopards are available in the Scenario Editor. But yeah, every animal added after RoR is not there, and herdables never appear in the official random maps.
I created a related thread:
Return of Rome - what I would change to make it feel “complete”
It’s not about new civs (and honestly, I don’t have high hopes for them right now), more about rounding out what already have (or used to have before Return of Rome).