Finding Worm Gear to fit to Motor For Sumo Robot

[brandnewself]

hello ! i need help for my Final Year Project. my group are making a sumo robot for competition , we had plan out the casing and get the part we need. We plan to make our robot unable to push back by opponents sumo robot so , we decided to think of worm gear. i searched online for worm gear box that able to fit to our motor and cant get any result.

Our motor for the robot look like this

http://lincolnrobotics.wikispaces.com/file/view/XL_TETRIX152rpmMotor.jpg/93069228/XL_TETRIX152rpmMotor.jpg

can any 1 help me to search for worm gear box for this type of motor ?