Gnomeregan Mechanostrider can be purchased for 100 from Rillie Spindlenut <Gnomeregan Quartermaster> at the Argent Tournament. You must be a gnome, or have completed [Champion of Gnomeregan] to have access to the quartermaster.
Patch 3.1.2 (2009-05-19): Renamed "Gnomeregan Mechanostrider". The [Turbostrider] can now be purchased for 500 5 .
Patch 3.1.0 (2009-04-14): Added.