The guy I kinda know can do it. They can bore up to 15" deep in house, so entire barrels is totally possible. The tighter the tolerances, the higher the price, but they could do it in the .0001" range if needed (overkill for us) I know you mensioned 9" long inserts, is that the number you still want? If you send him a barrel I think he could also freak bore it that deep. I have no idea on cost, but I'll ask once you know what you want done.
I race toy cars, and you though paintball was expensive... Rcjunky's feedback