Perhaps you can try JAL from NRT to SYD or MEL - they release 2 seats per flight at 10am Japan time each day, and generally easy to obtain (especially on the MEL flight) - and then you can just book the short trans-Tasman separately.
AS doesn’t publish a chart for JL to Australia (or Europe), so can’t get all the way there on JL. One of the limitations of Mileage Plan.