The Alliance bike built for Azeroth Choppers is now available in World of Warcraft. Alliance characters can purchase this mount from Paulie in Stormwind's Old Town district for the premium price of 100,000g.
Once you've purchased this masterful machine, you'll find it in your mounts list by the name Champion's Treadblade. As a reminder, the winning Horde Chopper was added to the game with patch 6.0.2 and was given for free to players who logged in between July 24 and September 30, 2014.
Remember, only characters of the associated faction are able to ride each bike, so buyer beware!