This mount is a quest reward from the quest  exalted with the faction Netherwing to obtain the quest and the right to purchase the mount.. It can also be bought from Drake Dealer Hurlunk on Netherwing Ledge in Shadowmoon Valley for 200. You must be
Edit: The Azure Netherwing Drake is now able to be flown in Azeroth, as well as Northrend and Outland.
It appears players who are in a guild level 24 or higher and have the Bartering guild perk will gain an additional 10% discount, lowering the overall price to 180 gold.