Hi Chris
Your socket looks like (is) a Neutrik Brand 4 Pole Speakon style speaker connector used in AV. The best bet would be to visit your local Jaycar store in person and have a look as there are a few types available: one a straight in line connector and one a right angle connector plug. You can also test fit the plug to be 110% sure. See details in the links below....
Neutrik 4 Pole InLine Speakon Connector Plug
https://www.jaycar.com.au/4-pole-inline-neutrik-speakon-loudspeaker-connector/p/PP1090?gclid=Cj0KCQiA7NKBBhDBARIsAH bXCB5AsslpoYIOG6Gdd5UlxXwd3LFEf93e5 BAfpIdQQ4pf_pwiSObo4nAaAp2EEALw_wcB
Neutrik 4 Pole Right Angle Speakon Connector Plug
https://www.jaycar.com.au/neutrik-4-...ector/p/PP1091
There is also a cheaper generic plug, but Neutrik is the original and the same brand as your socket.
Not sure about the closest Jaycar to Clifton Springs.
EDIT: (
I hate not knowing 
: It's Jaycar Geelong: 48 Mercer St according to their website)
Best
JA