There are plenty of folks that re-bore barrels but it generally does cost more than a new barrel. Ususally only a viable (cost effective) option for old or collectable guns that you want to get up and shooting (where factory barrels aren't available or you want to keep the "original" barrel on the gun).

Randall Redman did one for me years ago - good work but pricey and long lead time.

http://www.redmansrifling.com/