I've compiled a Google Calendar of the brevets and other LD events in the Northeast - primarily in areas within easy travel distance of my Vermont homebase.
This is a work in progress - I'll be adding to it as I have time - potentially including some centuries that will be great tune-ups between events. You'll need to scroll ahead to April - March to start seeing events. If anyone else wants to assemble a calendar for their region post a link here - Google users can overlay any number of calendars and see how things line up.
Also, I found the ORR and SIR schedules by doing a search.
Anyone can view the calendars, and if you have a Google account you can overlay any number of calendars with your personal calendar - which I've found to be very helpful watching work / life / play collide. (working on a running event calendar for my wife)