It's tricky, just like all registrar positions tend to be (in something that isn't FM or rural FM).
How familiar are you with the Australian training system?
Essentially it goes:
Grad from med school --> hospital house officer rotations (what the Aussies call residency, but you're not on any program officially to finish) --> registrar (enrolling with a college, in order to become board certified) --> fellow/attending etc. Becoming a Doctor
For IMGs to Australia you must sit the AMC exams. The first is MCQ, the other is a set of live clinical exams. The USMLE steps are not accepted as equivalent.
Only then can you be considered for rads.
Check out the official website. A Career in Clinical Radiology | RANZCR
Note that you must:
1. Apply and be accepted into the Royal College.
2. Also apply separately to an Australian hospital and be accepted.
3. Must be pgy2 to apply... again to do with the Aus training model. Like saying you must do two prelim years in something else, domestic Aussies usually pick surg.
Rads is (as you've probably guessed) a competitive field, with Australian domestic grads having a challenging time getting on. It is easier to find a rural hospital that is desperate to hire. At tertiary sites, generally, it requires rotating at least a few months before they will even consider you. They prefer to hire who they know, no surprises there. Unless you get lucky. Connections (to get those LORs) always matter.