Hey there,
From experience (Music 2 HSC 2009), I have many peers also struggled with finding an ""identity" that associatd their compositions with contemporary Australian music.
However, there really isn't a criteria that measures how "Australian" your piece is.
Instead, go out there and listen to as many contemporary Australian composers and do a quick analysis on the standout features of each piece.
Such details could be:
Rythmic patterns - Weird time signatures, Synchopated rythms, free rythms,
Combination of tone colours - colour chords, unconventional harmonies, polychords,
FUSION music - Combining music from different cultures and background,
Structure - Conventional structure with chorus, through composed
Timbre - Unconventional playing techniques
The key in creating a successful composition for this section is taking INSPIRATION from Australian composers and DEVELOPING and REINTERPRETING these details.
Hope this reply has been of some help to you.