Green’s Dictionary of Slang

(Aus.) formal dress worn by functionaries, e.g. for a Royal visit .

1962		Canberra Times (ACT) 14 Sept. 9/2: The Northern Territory people will greet the Queen and Prince Philip in ‘Darwin rig.’ This is the local formal dress of black trousers and shoes, white shirt and black tie.
1993		Aus. Word Map 🌐 ‘Territory Rig in my experience in the Top End is generally refering to the tropical beauracrats look of the 70s/80s of collared short sleeve shirt, longish shorts, and long socks!’.