I can't find replacement wheels for a kid's small aluminum K2 scooter. Wal-Mart and Meijers don't carry them.

most are Roller blade wheels, try a roller blade shop skate shop or search the net for inline skate wheels,

try a drug store...was surprised myself to be sent to a drug store...it seems that the small wheel is also used as a guide wheel on some mobility's scooters...and they ordered one