We usually go in September and from memory the earliest Ive booked is about March of that year. But if you find a package you like you can always ask the agent what it would be for Sept, but then you run the risk of missing out on some great deals.
We have been in September and are planning on going next August/Sept. The deals come out in Feb/March. We have used Holiday Specialists to book our last two Pacific holidays, one to Fiji and one to Vanuatu, they have great deals.