They're a little heavy but I like them.
http://www.robotmarketplace.com/prod...on_wheels.html
All you have to do for a hub is take some aluminum round bar, turn it to size (for a press fit), knurl it, drill and ream it, part it off, and broach it, and press it in. If you do it right, the hub doesn't even need a flange on it;, just a straight cylinder through the wheel's bore.
They're not the absolute grippiest tire out there, but they grip rather well and wear well. They'll last all season long even driving on pavement, parade routes, demos, etc. The zero-maintenance aspect was my reason for using them last season. I'm over having to rivet on conveyor belt tread.
Just beware if you attempt to machine the wheels themselves. They may have small air pocket voids inside from the molding process.