I live in New Hampshire, and there's a Montessori school near where I live (Concord) taught and owned by Capitalists, Objectivists, Libertarians and Free State Project members
Now that sounds like a school I would feel comfortable sending my kids to.
Then get yourself to NH ASAP, man!
What do Libertarians generally think of Montessori schools?
Well, Libertarians in general are for privatization of schools, and as far as I know, there aren't any (or damn few) Montessori-style Government-Run schools. I really like what I've seen about the Montessori concept, especially for grade school-age kids, but that's not really because of anything Libertarian. My statist, NEA-card-carrying aunt was a teacher for 20+ years and she raves about Montessori as well.
Then again, maybe there is something fundamentally Libertarian about Montessori; it does let on the children focus on the areas they find most interesting, and explicitly does not have the notion of a hyper-structured "1 hour of english; 1 hour of math; 1 hour of history...."