Alludra the Mage here dropping in from the sky to steal that pet!
5.1 has dropped. This patch has been a pet battler's dream with tons of new pets, new quests, and the best part pet battle stones!
These stones come in two types, polished battle stone and flawless. The polished battle stones will upgrade your pet to green quality, while the flawless battle-stones will upgrade your pet to rare quality!
Sounds awesome right? Well there's also the catch that most of these flawless battle stones are family specific, annnd they aren't that easy to find. You see you can get them in battles if your team takes down pets with higher levels or they can be found in the satchel of goods from battle trainer dailies. Personally I haven't found one yet, but I've got patience.
I do hear that you can 'farm' up the stones you want in wild battles by picking the type of pet you want the stones for by battling them specifically, but as I said, I haven't gotten one myself so I am not sure how this works in action.
What I can say after buying over priced rocks on the AH and turning my gray minfernal into an amazing rare powerhouse is that they are totally worth it for those rare spawn pets whom you just can't seem to find a rare of!
But that still leaves a lot of my pets out in the cold so if you'll excuse me I have a lot more battling to do!