In order to get this mount, you need to become exalted with the new faction Talon's Vengeance. This is a harpy faction located in Highmountain, and is somewhat tied to PvP. It is currently unknown how to farm rep with them, but this guide will be updated once more information surface.
Once you hit exalted with Talon's Vengeance, you can purchase the mount from a vendor called Trinket, which is located in Highmountain. It has a price tag of 10 000g .