Do a search online. Plenty will come up. Baseballweb will have them. Hard to find stores that carry them although the Shells Sporting Goods by us do carry some…but just 10 and 12 oz balls. I have found some at used sporting goods stores (Play It Again Sports) ranging from 4 oz to 16 oz. That is hit and miss of course.
Kyleb that is active on this site (his site is Drivelinebaseball) sells high quality weighted balls…a good way to get a complete set at a resonable price.