google is your friend.
never been to Montana, but its just my guess that there isn't a spot that hasn't been surveyed by the USGS, google the maps, it'll be marked.
or all the archeology maps that have been done, should have quarry sites marked.
I'm not a geologist, and I'm not sure but I don't think a geologist could predict exactly where to find a flint outcrop, may or should be able to tell you an area, but I would think that would be it.
the flint on top is going to be freeze fractured and worthless, except for maybe strikers. gonna have to do a bit of digging to get to better flint in Montana, is my guess.
I have a bit of experience with this, take multiple pairs of leather work gloves, don't go crazy on the price, they'll be trashed after you get done.
an old truck or car leaf spring works great as a pry bar to get between the plates.
safety glasses and a small sledge, and a heavy spud bar and a large copper baton for spawling the large pieces as you get them out to lighten the load.
several 5/five gallon buckets, when you think you have enough add a few more, just in case.
a 5/five gallon bucket of flint, 75-100 Lbs. depends on how small the pieces. strikers--upper end, large blades-- lower end.
have fun.