What about a POD that sees a lot lower amount of white immigration flowing into Australia, combined with a much larger Aboriginal population (perhaps the Aborigines have better resistance to disease?)? In this ATL Australia, Aboriginals are maybe 20% of the population, but still an oppressed and much poorer minority. The USSR and Maoist China funnel arms, aid and diplomatic support to extreme left Aboriginal factions. There is also support from extreme left wing white Australians in support of their Aboriginal comrades. The US and West of course, fully support the Australian Government.
The far left will be eventually crushed of course, as the whites are more numerous and better armed. But for a while at least, you'd have a nasty Cold War insurgency with atrocities on both sides.