I spent a some days in Coober Pedy a few years ago. It is a fascinating place where there are, as you say, loads of older Brit wagons. Most are still goers as they are used to transport the ginormous boring machines used by the miners. So they only need to move occasionally and then for short distances.
Don´t forget that prior to the UK joining the EU Oz was a massive supplier and customer of the UK, thus the loads of older British gear about. Since we abandoned them the Pacific rim countries have taken our place.