The easiest way is going to guild towns, if you find a crystal, you can destroy it and blue chests will spawn, when destroyed, they drop pet food, exp/cp charms, and other stuff.
Alternatively, you could buy it from the item mall, or the loyalty shop.
Also, you could get another pet from making an alt do the level 5 quest and archive the new pet with 100 durability.
If you want to save durability, you should know that it will lose it when equipped, regardless of if you use it for combat or anything, but unequipped it doesn't lose any durability.