The Darkmoon Faire - a monthly event that lasts for a whole week and hosts a large variety of fun and games - also contains two pet battle dailies.
The fights against Christoph vonFeasel and Jeremy Feasel (who in reality is also the designer at Blizzard responsible for the pet battle systems), can both be used to level a pet very nicely. They also give a satchel which has a chance to contain one of their pets each:
Syd the Squid
The drop chance is rather low but you can also buy them on the AH if you prefer. In any way, I wish you good luck in acquiring them!