I believe Montana Rifleman (like the Winchester Custom Shop) get their octagon rifle barrels from Badger Barrels. They make only "match quality" barrels and they are available in several contours. I think barrels for the Ruger #1 are listed on their website. Search "Badger barrels" for more info.

Really most of the barrel makers will provide an octogan barrel. Lilja, Kreiger, Badger, Montana rifle, Bench Mark.... Just ask. But if the barrel maker that you want to use will not do it then call Mark Straton. He does a great job and will do it quickly. Michael