They have a facebook page:https://www.facebook.com/cayecaulkerlobsterfest?fref=ts
I agree, Caye Caulker is WAAAAYYYYYY behind in marketing this event every year. They don't decide on a date until one month or so before the event, although the dates are quite predictable. The Fest usually ends up being the last weekend in June.
Maybe someone at the facebook page will be more helpful?
Good luck with getting more information.