WOA does sell only finished barrels.
But Krieger & many others will sell you a rifled cylindrical blank that you must do all the finishing on including clambering & installing the barrel extension.

Should be no problem for one of your skill.

Or buy a finished barrel from CLE with one of their 4 different chamber options.......Frank White & his team really do know a thing or 2 about barrels & chambering them right. He has blanks from Bartlien, Krieger, Douglas & Criterion.

MM