It is interesting to observe that there isn’t much of a tradition of patriotic and memorial classical music in Australia. Looking around I came across very little so I’d be happy to hear from anybody who knows of any, particularly if it related to the Anzacs. The only specific piece I came across was by Miriam Hyde: Anzac Threnody for voice and piano.
I would however like to nominate a piece as a candidate. Symphony No.1 or Da Pacem Domine by Ross Edwards was not specifically written about the Anzac experience but it was at least in part a reflection on war, in this case the Gulf War, in addition to being dedicated to Stuart Challender. David Porcelijn has conducted a recording by the Sydney Symphony Orchestra.