(There are many books of Montessori's talks and writings. These are just some of them.)
Association Montessori Internationale, founded in 1929 by Dr. Maria Montessori: montessori-ami.org
North American Montessori Teachers' Association: montessori-namta.org
Montessori Teacher Training is available in Atlanta at www.montessori-imti.org and at info@montessori-mia.org
The Michael Olaf Montessori Company provides practical advice for using Montessori philosophy in all kinds of settings. Since 1982 it has been a favorite source.
The Michael Olaf publications are available to be read online as well as ordered. This can be done at michaelolaf.net.
The International Montessori Index