I'm not sure that the bylaws for a Montessori school would be much different from any other public or private school's bylaws. I haven't seen much discussion on the boards that is specific to Montessori, so if you don't get a response here or need more info than you get, I would suggest visiting this web site www.montessori.org/search/SearchUSSchool.htm.
You can locate schools in your area and contact them to find out if any have PTO's that would be willing to mentor your group in the process.
WE are starting up a brand new PTO for our NEW montessroy school beginning in 2005-2006 school year. I am wondering if anyone out there is in a "Montessory school" and already has some bylaws we can look over in order to get ours started up