I get mine from [link=http://stores.ebay.com/WalawalaStore]here[/link]

They are plastic safe and they sell bearing sets for specific tank sets.

Btw in this [link=http://stores.ebay.com/WalawalaStore/Balls-and-Bearings-Lubrication.html]link[/link] they do saythey are plastic safe, anyway another member form my club have been usingthem for 4 years and have not come into any issues with the bearings being plastic safe or not