I've noticed the academic year planners are starting to emerge.
LoveNotebooks has Paperblanks academic year planners available now.
Simply Moleskine has some of their 18 month planners in stock now, but Amazon lists them as being available in April or May.
**Edited to add: Today my large 18 month 2015-2016 Moleskine weekly notebook (in the gorgeous new Tide Green color) arrived, and I was very pleasantly surprised to find they have gone back to the grid monthly calendars they used several years ago! The only problem with these is they sacrifice the future-year planning that was in the monthly columns. But honestly there are plenty of notes pages in the back of the book to convert a few into your future-year planner.
Quo Vadis academic year planners are usually available in May, as are most of the other brands.
Do you use an academic year planner? How early do you like to buy yours?