Black Hole Weaponry/Columbia River Arms still sell 264 LBC chambered barrels to use .125 bolt face x39 bolts. JSE Surplus also sold barrels chambered to use .125 bolts. I read some of the JSE barrels were manufactured by Wilson Arms and some were manufactured by Marlin (JSE House brand). Id be concerned the barrel extension might not fit the KS47 bolt as it might be a proprietary design.
http://www.jsesurplus.com/barrels65.aspx
http://www.jsesurplus.com/barrels65.aspx