I dunno what a new barrel would cost, but you could send it to SumToy and get him to cut it to the exact length you want, thread it for one of his chokes, and then make you a choke. Probably run about $100 for all that. His chokes are built like a tank.

http://www.sumtoycustoms.com/index.php/prices


All the labor of man is for his mouth, and yet the appetite is not filled.