WTB: Colt Pencil Barrel or Upper with FSB

WTB Colt 6320 / 6520 / 6720 / sporter or similar carbine gas pencil barrel with fsb, 10-16" as long as gas port hasn't been opened above .070 ; May also consider bushmaster pencil fsb barrel or H&R TIA 10-10.5" barrel / upper.