Oh man, that's terrible.
You have to get these on the shelves for at the very latest October 1st (most are up I'm guessing in early September). Factor in six weeks to print and distribute and the latest you can push this is mid-August. But most of these calendar companies are probably small-fry and need to get these printing earlier. That being said, everyone in the world knows that teams get shuffled on July 1st so at least make the final call in mid-July!
If you post a picture of that calendar page, I can tweet it and maybe it will go viral