The Warbot and its assorted fuels were originally part of a U.S.-only Mountain Dew Game Fuel promotion back in 2009. For those wondering what the heck the fuel is for, you can load your robot up with either Horde red or Alliance blue fuel, and Warbots that have opposing colors of fuel will battle each other when in proximity. It was a fun promotion, but the lack of availability for anyone not in the United States was a bummer, so it's nice to see the Warbot available to all at last.
To purchase your Warbot, just head to any toy vendor. The Warbot costs 500g, but it is affected by reputation; exalted reputation cuts the price down to a slightly more affordable 350g. As for the War Fuels, you can pick whichever color you like, regardless of what faction you happen to be on. Happy battling!