Hi Graham
I live on the south coast of NSW, so at least I am only on the other side of the country. :)

Don't assume that you need strips the length of the kayak. There are some builders, including me, who deliberately avoid using long strips. I find them difficult to handle and when it gets to the point where I have to taper both ends of the strip, I have no margin for error. I have built 4.5 to 6.4 metre kayaks mostly using 1.8, 2.4 , 3 and 3.3 metre strips. I do all the scarfing (except for the sheerstrip) as the strip is fitted on the forms.

Don't assume that you need new timber. The deck of a kayak I made for my son-in-law was almost entirely made of strips ripped from WRC lining boards I had pulled of his bathroom wall when I helped renovate their house. The deck of my Night Heron Double is almost all old redwood skirting boards. The hull of the first two kayaks was made of strips ripped from the scraps cut off the huge WRC boards by the timberyard when they ripped them down into normal size boards.

Tassie Oak is far too heavy for a kayak. So is most pine. However, the effect of water on the timber is not relevant because the timber is completely encased in glass and resin.

The timber I use most, especially on the hulls of my kayaks is Paulownia. I don't know if it is grown in WA. I get mine from a plantation in Tyalgum in northern NSW.
http://www.paulownia-timber-sales.com.au/aboutus.html
I have bought timber from John White for about half a dozen kayaks and find him very helpful. It is about 20% lighter than WRC, so saves a worthwhile amount of weight.

I have no idea what the freight costs from NSW to WA would be, but it might be worth investigating if Paulownia is not available in WA.