|Farming Azure Whelplings|
Azure Whelpling companion pet can drop in 2 places only.
Azure Whelpling drop location changed
Pre-cataclysm, Azure Whelplings were obtained from blue dragonkin only. After Cataclysm, Azure Whelpling companion pet now drops from any monster in Winterspring. Although rare monsters have a slightly better chance at dropping this. Visit Loot Hunter for all you need to know about rare spawns in Winterspring. Winterspring is a level 50+ zone, so make sure your toon is strong enough.
Misty Satchel of Exotic Mysteries was also added to the game some time ago, and it may also contain Azure Whelpling, although it's such a low drop chance, it's faster to obtain it if you just farm it by killing things, instead of queueing as a tank or healer.
Where is the best place to farm it?
As for a specific farming spot, I cannot recommend any. The areas that contain the most mobs are obviously the fastest way to get an Azure Whelpling. However, with Cross Realm Zones introduced, these spots are often infested by bots. That said, there's no point sticking to a specific spot, unless it's a player of the opposing faction so you can encourage them to log out ;)
Here's the Top-5 killed monsters that can drop an Azure Whelpling:
Click here if you want to read about it.
Found it! How much should I sell it for?
If there is no one else selling Azure Whelplings, you're in luck! You can decide the price yourself now. It's average price on wowhead is 13,000 gold. That is a good amount to start with, and reduce it bit by bit until a pet collector sees it and deems the price fair enough.
If you are not the only seller, let the undercutting begin! (Or stash the pet in the bank for a week)