Search the map to find a Crocodile Lair (generally look near water), I went in Faiyum Oasis (Eastern side of the map). Then use Senu to try and find a Lion or Lioness nearby. You must have both the Sleep Darts and Animal Taming Abilities unlocked. Simply put the Lion to sleep, tame it and bring it to the Crocodile Lair (or wherever you found your crocodile (again, Senu is a great help to try and find it).
I created this video to help:
Hope this helps.