This mount is a quest reward from the quest  . It can also be bought from Drake Dealer Hurlunk on Netherwing Ledge in Shadowmoon Valley for 200. You must be exalted with the faction Netherwing to obtain the quest and the right to purchase the mount.
Edit: The Veridian Netherwing Drake is now able to be flown in Azeroth, as well as Northrend and Outland.
- The exalted reputation faction discount does not apply to Drake Dealer Hurlunk as he is not tagged as part of the Netherwing faction.