super short M4 outer barrel

[infernau]

Does anyone know where I can get a 4" (total length) outer barrel. I want the barrel to receed a silencer just under a classic army seal cqb front rail. the best I've found is through ebairsoft at 13.5 cm (10 cm would work).

Any help would be great, I've spent nearly an hour looking at google images to find one with no success and before I get the one I have milled down and rethreaded I figured I should see if someone has had better luck than me.

Thanks