Hi, Jennifer!
Fantasmic! Dining Experiences tend to be released just a tad bit later than park calendars and other types of dining reservations. I'm waiting for July dates to be released as we "speak"!
I've noticed over the years that, as one month comes to a close (January!), another will soon be added to the Fantasmic! Dining Experiences, so keep checking back on
Walt Disney World's Dining & Reservations page, under "Dining Event." If you keep an eye on that site, and the date you'd like, calling or registering online as soon as the dates have been updated, you should be just fine.
...and I'll be right behind you in line for a reservation for a three-generation trip in July!
Best of luck with your dining reservation! It's a great package, to be sure!
Come back with any additional question you may have regarding your upcoming trip to Walt Disney World! I love to help!