The X-51 Nether-Rocket X-TREME is a piece of loot available from the trading card game set Servants of the Betrayer redeemable from Landro Longshot in Booty Bay.
In Mists of Pandaria, it was added to the Black Market Auction House. It can be listed by Landro Longshot for the opening bid of 15,000.
A goblin falling off the X-51 Nether-Rocket
The rocket mount on the right of an art piece.