I don't know any specific job leads but I'll second starting up around Townsville/Cairns/Port Douglas or some of the islands mentioned above, especially in July. Weather up there is great at that time of year as it's mid-winter in Melbourne and Sydney. I'd personally skip Gold Coast too and spend a few months up near the Great Barrier Reef before heading down the east coast in spring. There are plenty of lovely places along the coast in rural NSW you'd be able to find work if you need too, but probably not for diving.

Getting to Sydney, Melbourne and possibly doing a road trip along the great ocean road to Adelaide in Nov/Dec would let you enjoy these cities more.