you got no choice, gotta buy off the net. there's a certain american one that can get them here cheaper including shipping seeing as the exchange rate is pretty even e.g:$1 aus=93c usd
that would of been seb and they're shitty plastic wheels. the metalcores are 65 75
These are the cheapest in australia. You can buy em from here.
http://wonniescooterproducts.weebly.com/wheels.html