Talk with Ken Farrell. I see on his website that he makes Bases for the Montana action. The most i have seen is 20moa. I had him make a 40moa base for me for a Geske action and it only cost me $100 but i see he raised his prices to $135 for custom bases.
I am toatally satisfied with his product and will use his services in the future. Great guy to talk to.