Vex, your going to have to design some sort of bracket and hubs to connect to their wheels.
Andymark, the wheels from them were ment for an FTC bot, and have the hole pattern already for an axle hub, so those would be the easiest to mount. Granted, I have heard teams have been snapping the rollers off of these with semi-normal use.
There is one last mechanum wheel out there that I have seen being used, but the cost of them is through the roof, which you probably dont want to be having to buy for an off-season project. These are really stong wheels though, as the structure is made of metal and not plastic. And again, with this one, you would have to make/print some sort of bracket and hub.
https://www.superdroidrobots.com/sho...px?itemid=1352
For testing purposes, I would go with andymark. Thats what we are doing. Even though we will probabaly stick with the regular 6 to 8 wheel tank drive for competition, as when you get to the World Championship level, you need that torque and defense, otherwise you will not have fun.