http://www.crasseux.com/criticalmass/

Another site chronicling Critical Mass events in Montreal

http://enwoyeonavance.org 

A collaborative Wiki for the event in Montreal

http://critical-mass.info/

A comprehensive index of rides around the world

http://www.critical-mass.org/

Another world index

Just about every city has at least one website dedicated to the Critical Mass that happens there. A quick Google search should turn  up the one you're looking for.