AutumnnShandris' Comments

Desert Spiders can be found in groups of 3 in the Cradle of the Ancients and scattered in many locations through the desert and in the temples.

Just tamed a lvl 23 Rare in Uldum. They are scattered throughout the zone.

Squirrel also spawns in Sholazar Basin level 21. I have seen 2 spawn there as main battle pets.

These can spawn anywhere there is green in Sholazar Basin. They can also appear as a secondary battle pet to any of the other pets in  Sholazar. The spawns in Sholazar Basin do not appear to be linked to any time or weather marker.

Found everywhere the adult Dragonbone Condors are. Found both flying and sitting on the bone carcasses. Secondary pets are Strand Crab, Tundra Penguin, and Arctic Hare.

I also have seen them when on a flight path but went back and saw nothing both on toons that were loremaster and no quests done. I logged in right after a server reset on a quest-less toon and lots were spawned. Took about 10-15 spawns to finally get a rare. Every whelp had cockroachs as secondary pets.