The airports are where the dramas begin.
I can't recall what MA does, but CAMS have a log book system for owners of historic vehicles. Some airport staff are highly dubious of even this, and will still refuse to sell to sell you avgas.
For better or for worse, Australia is far more heavily regulated than the USA, particularly when it comes to things like fuel and aviation. While some people live in areas (typically rural areas) where they're a lot more easy-going, the majority of us simply don't have easy, reliable access to avgas.
The choice to use fuels other than avgas, is not simply for a lack of trying.