StB have only the one DZ in WA last I heard, unless calling their temporary DZs at Rockingham and Langley Park qualifies, and if that is so then the other operators also have several DZs where they drop into.
Jurien Bay, Busselton, Pinjarra, Hillman (when they operate) and I'm not sure if there is still one in the Pilbara are all separate.
On the other hand StB seem to be cornering the market on the east coast, but 90% of the market is a tad over stated (although I'm sure they are trying).
Given that most of their operations are turbine I guess that will give a starter as to what would be required to get into it apart from the total hours in command and hours on type etc.