Lengthening Adapter/Muzzle Device for 11" barrel?

[jujubeez]

Anyone know of any 1/2-28 barrel adapters like the ones in the link but that can accept a muzzle device. Or some not so goofy looking extended muzzle devices? I need at least 5.5" but preferably 6" extended.

http://mfiap.com/i-21260033-mfi-m4-socom-adapters.html

Thanks