From the list of Montessori Schools registered with the Montessori Schools Association and listed on the Montessori St Nicholas Charity website, with a little text processing, and the help of Google Fusion Tables, I created the below map of Montessori Schools.

https://www.google.com/fusiontables/embedviz?q=select+col4+from+1niWxiDXEY0ceIRgJwo7_zCTVTHffdVFvt3BXTCM&viz=MAP&h=false&lat=54.66264091468062&lng=-362.90120251875&t=1&z=6&l=col4

Each node on the map is clickable, and provides a link to more details from the above site, as well as whether the school has acheived any accreditation from MSA.