For extensive information about the Gurdjieff teaching, G. I. Gurdjieff, and centers worldwide for the study of his teaching, the best online resource is the Gurdjieff International Review. While that site periodically adds new and valuable content, the following articles are especially informative:
"The Look from Above" by Jeanne de Salzmann
"G.I. Gurdjieff and his School" by Jacob Needleman
"Gurdjieff Observed" by Roger Lipsey
"Sacred Dance: The Search for Conscious Harmony," an interview with Pauline de Dampierre
"The Holy War" by René Daumal
The Study and Research Center for Knowledge of Man, founded by Henri Tracol
Gurdjieff Foundation of New York
Gurdjieff Society of California (San Francisco)
Gurdjieff Society of Washington, D. C.
Gurdjieff Society of Philadelphia
Gurdjieff Society of Atlantic Canada
Many other affiliated centers in North America can be found here: Gurdjieff Foundation of New York.
Centers worldwide can be found here: International Gurdjieff Foundations