What year series AU?
You can buy new ignition barrels from Nice Products
e.g.
https://niceproducts.com.au/feature/search-by-vehicle/ and
https://niceproducts.com.au/feature/search-by-vehicle/
But it's usually the actual lock rather than the barrel the breaks and, if so, you will indeed need a complete new second-hand lock assembly which often does mean buying the whole column from a wrecker and they are getting harder to find.
You could try the people that do these
https://fordignitionswitch.com.au/#buynow and
https://www.frk1.com.au/ but I don't believe they have a kit for the series I AU and perhaps not the later series AU's either. In any event it sounds like your lock is broken in a different way (as the AU, EL and EF did) and a used lock assemble is required.