After a quick bit of Googleing, I found this one:
http://www.rcmart.com/cp002-pistol-g...r-p-17151.html
Obviously, something like that is probably going to be your best bet, especially if it's 'plug and play' with Windows. A COTS controller should be significantly more reliable than something 'custom made' without extensive testing and all of the fun things associated with that.
You can also look into making a custom controller (or modifying an existing one) that will with with the Driver's Station using an interface like
E-Stop Robotics "CCI". Modifying an existing controller to work with the CCI shouldn't be too hard, simply take the leads from the throttle and steering inputs (usually a variable resistor of some sort?) and wire them into the analog inputs on the CCI. If I were to pursue this route, I'd make sure that the controller were well tested and it's reliability proven before ever using it at a competition.