It is not Australian, as far as I know, but it came with the Australia tape, which I have removed. No other tags or stampings.
It is cut like the US ERDL Combat shirts used in VN , but made of HBT material, not ripstop material ; most likely a commercial item.
It has Velcro fasteners on the pockets which would indicate 70s- 80s vintage. The pattern is unknown to me.
Anyone have any input ?