In a pinch you can adapt the forend for the 14" barrel by using only one screw and inletting the unused screw socket. There is a special longer wood and composit forarm available from their custom shop Fox Ridge. http://www.foxridgeoutfitters.com
If you're working with the rubber Pachmayr forarm, which utilizes a special hanger to attach the forarm, I'm not aware of any Pachmayr forarm specifically made to fit the carbine.