Our team has had great sucess using the NPC Robotics wheels. They are simalar to colsons, however come ready with a .5" bore w/ 1/8" keyway. We personally use the 6" variety, but (correct me if I'm wrong)
team 148 used the 4" wheels this year on their swerve modules.
You can get them either at:
NPC Robotics
Robot Marketplace
Both sites have them for $19 a piece, which from what I have seen, is nice a cheap!
Good Luck.
-Chuck