Pacific National (freight but hauls 'Indian Pacific', 'The Ghan', 'The Overland' and 'Great Southern' passenger trains) and Aurizon among others tend to be constantly looking for qualified locomotive drivers (NB: not 'units' or as we call them 'railcars').
Here's an example from the Seek website in Australia - at a very quick look, it also had vacancies in Adelaide, South Australia. (Kalgoorlie is a gold mining town in Western Australia, and is on the busy transcontinental railway with many intermodal trains from Melbourne, Adelaide and Sydney/Parkes.) There's also a lot of minerals in WA hauled by rail, not just in the Pilbara that's isolated way up northwest (major centres there include Port Hedland).
Aurizon
West Kalgoorlie, Kalgoorlie, Goldfields & Esperance WA
Rail & Maritime Transport (Manufacturing, Transport & Logistics)
Full time
Great Salary + $15k Sign on / Retention Payment
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I haven't run the numbers on living costs in Australia v England, but salaries these Australian train drivers earn should be way above UK levels, allowing for the weak Australian 'Pacific peso'.
Unfortunately you'd almost certainly have to start from zero with driving, and naturally be able to emigrate to Oz. But as others have said, you'd have many transferable skills.
There tend to constantly be vacancies for coal train drivers in Central Queensland and sometimes the Hunter Valley, NSW (latter close to Newcastle, 160km north of Sydney).