Highly unlikely. There is just no reason or need for any Dash 9's to be airfreighted to Australia from the U.S. The charter cost over that distance would be astronomical.
They are West Australian Iron Ore loco's .. the Iron Ore Co's plan ahead, and any imported from the U.S. (new or used) are shipped by sea.
Can't even recall an AN225 ever landing at Perth .. however my memory has been faulty, once ..
Maybe this is one you're thinking of?? ..
http://www.historyofaircargo.com/i-T...ane-takes.html