Here is the information that I found :
While you will still be able use your regular pets that you already own, Mists of Pandaria introduces new random spawns across the world known as wild pets to add to your collection.
-Zones have unique wild pet spawns that are zone specific--for example, a Dusk Spiderling is unique to Duskwood. Similarly, a Tiny Harvester can only be found in the farm fields of Westfall!
-Every zone also has more common ones that you can catch in multiple zones. You can find tons of Rats everywhere, for example.
-There are also extremely rare wild pets specific to zones, such as a named parrot called Polly in Stranglethorn Vale. These can also have conditionals applied to them: outside of Karazhan, a ghost called Restless Shadeling spawns only in the early morning.
-You are able to track and find these pets through a new UI feature
Blasted Lands
-Fire Beetle
-Spider
-Adder
-Scorpion
-Scorpling
-Restless Shadeling (only available at night)
-Swamp of Sorrows
-Water Snake
-Toad
-Parrot
-Moccasin
-Swamp Moth
-Huge Toad
Duskwood
-Black Rat
-Rat Snake
-Roach
-Mouse
-Skunk
-Dusk Spiderling
-Widow Hatchling
Westfall
-Snake
-Prairie Dog
-Mouse
-Tiny Harvester
-Shore Crab
Elwynn Forest
-Small Frog
-Squirrel
-Rabbit
-Fawn
-Black Sheep
Loch Modan
-Little Black Ram
-Squirrel
-Rat
-Ram
-Small Frog
-Snake
-Sheep
Redridge Mountains
-Mountain Cottontail
-Redridge Rat
-Roach
-Fledgling Buzzard
Both Stranglethorn Vale's
-Tree Python
-Beetle
-Forest Spiderling
-Lizard Hatchling
-Parrot
-Shore Crab
-Crimson Moth
-Polly
-Long-Tailed Mole
-Wharf Rat
Burning Steppes
-Lava Crab
-Lava Beetle
-Cockroach
-Scorpion
-Ash Viper
Badlands
-Spiky Lizard
-Rattlesnake
-Stripe-tailed Scorpion
-Gold Beetle
-King Snake
-Black Rat
-Beetle
Searing Gorge
-Ash Spiderling
-Fire Beetle
-Lava Crab
-Molten Hatchling
Dun Morogh
-Snow Cub
-Alpine Hare
Wetlands
-Squirrel
-Mountain Skunk
-Black Rat
-Mouse
-Cockroach
-Water Snake
-Toad
-Tiny Bog Beast
-Rat
-Prairie Dog
-Grasslands Cottontail
-Tiny Twister
Hillsbrad Foothills
-Deer
-Rabbit
-Red-tailed Chipmunk
-Toad
-Huge Toad
-Maggot
-Infested Bear Cub
-Spider
Western Plaguelands
-Squirrel
-Deer
-Rabbit
-Black Rat
-Undead Eagle
Eastern Plaguelands
-Festering Maggot
-Bat
-Infected Squirrel
-Infected Deer
-Black Rat
The Hinterlands
-Hare
-Maggot
-Rat
-Deer
-Cockroach
-Brown Marmot
-Jade Oozeling
And here is a picture of Polly one of the most rare pets.
