Here are my two suggestions (Paper base)
1. Use the tickler file for the two months before the meeting so you can plan. Personally, I would just use the template of the meeting inside the month folder as the OBVIOUS reminder.
2. Plan the 4 dates for the year a year out, tell everyone (if you have the power and authority) that these dates are non negotiable, and they are to plan their schedule around these pivotal (if indeed these are mission critical) dates. At this point, half the battle is won in my opinion.