Swap meet or early Ford club events. I'm not too familar with the Qld scene, but I wouldn't expect to find them at the major Qld military swap at Canungra, but more likely general Vintage vehicle gatherings like
Toowoomba in Feb or
Brisbane in May.
You find old car parts where you find them and pay what you agree to pay. Depending on condition, the wheels could be anywhere from $10 to $100. You might want to pay extra for a matching set of 4 or 5. Ask around and let people know you're looking. Keep an eye on Ebay, Gumtree and even the local tip recycling centre. Stuff shows up in the strangest places. Make sure you know how to tell the difference between 5 on 5 1/2 and 5 on 4 1/2 stud patterns.