The new ACMA system is in place and it seems that there are some issues with the initial deployment. Several current callsigns have started showing up as available. I have included 2 links here, the first is to the search facility of acma.
This second link is to the WIA available callsign lookup. Given that this is automatically built from ACMA data, the place for fixing is probably the ACMA.
More news as it comes to hand.