Try calling the BP fuels hotline 1300 139 700. They may be able to tell you who distributes it in your area.
Could try your local airport too, they'll have a few bowsers of AVGAS..........should be able to fill a jerry can there
I filled up the plane at work last week...........$1.27 litre. BP100 is AVGAS, just a different name for government tax purposes.