I just discovered this website. It’s very comprehensive, has many, if not all, of the Montessori lessons in every area of curriculum, not just math, for ages 6 - 9. I’ve looked it over a little bit. The lessons are the same as those I learned but unfortunately they aren’t illustrated. That might make it a little hard to understand some of them. However if you explore the sight, you’ll find the various materials and manipulatives described in other places.
The place value lessons are all there. I was describing these materials in the place value thread a page or two back on this forum.
http://www.moteaco.com/albums/math1.html
Click on Montessori Albums (Moteaco), then click on whatever area of the curriculum you’d like to explore.
It’s got great links to other Montessori and homeschooling info.