"Bannerman's to New South Wales?
Possible, I guess."
Bannerman bought sold literally all over the world. And, it's actually the most logical way for one of these rifles to have gotten there.
When the Soviets defaulted on the remaining contracts for the Mosin-Nagants, the US military stepped in, purchased virtually all of the remaining guns, and used them for training purposes to free up Springfields and Enfields for troops going to France.
After the war, Bannerman purchased something like 20,000 of these guns, or virtually all of the guns on which the Soviets had defaulted, from the US military.
Commercially, via post war surplus, is virtually the only way one of these guns could have gotten to Australia.
Given that the gun is in Australia, it's most likely that this is NOT one of the ones chambered in .30-06, although that is possible.
Not that many were rechambered for .30-06. Remington started loading 7.62x54 for the US commercial market right after the war, so ammo wasn't exactly scarce.
"The gift which I am sending you is called a dog, and is in fact the most precious and valuable possession of mankind" -Theodorus Gaza
Baby Jesus cries when the fat redneck doesn't have military-grade firepower.