Any five cages with caragors will do. Caragors are indicated by the three red slash marks. They are beasts that you can ride with a skill and are locked inside cages with a lock that you can melee or range to open. I personally got this during a mission early in the game, I believe it was the second main mission that I did. You help out an orc and you are basicall gifted four free caragors to free.