These are KMZ raster versions of the Geoscience Australia NatMap 250K 2008 dataset suitable for GoogleEarth and CustomMap compatible Garmin units. It is released under the CC BY 3.0 AU licence - please respect it.
You can use the interactive map below to zoom into an area of interest and it will bring up a link to the corresponding mapsheet. Alternatively if you know the name of the mapsheet you require you can browse the full list of available maps.
Standard mapsheets come out at 16 tiles so you can generally put 6 mapsheets onto a Garmin device (there is an annoying 100 tile maximum for Garmin CustomMap) but the special sheets around the coast vary from 11-35 so you may only be able to use 4-5. Enjoy...
Alternatively you can download the index sheet for viewing in Google Earth.
Hopefully one day Geoscience Australia will release the 100K data under the same licence but nothing seems to have happened with that since they pulled the product a couple of years ago.