Ok, so we're looking for a place in the southern pacific ocean area where it is possible to:
1) Hire windsurf kit, and
2) Be (virtually) guaranteed sailing wind of let's say 15 - 25 knots (it can be any time of the year) for a period of about 10 days (trade winds?)
Failing that, only number 2) with the proviso that you can you can fly there with kit (that limits the airlines you can use) - one board, one mast, one boom, two sails. Or in the case of WA, fly there and take a hire van if you need to.

So, for WA - what time of the year and where?
Anyone been to New Caledonia? Any of the other islands for sailing?
North Queensland - what are the jellyfish issues?
Where else?