Wow. I looked, on your behalf, for Australian-sourced full brisket and came up with zilch. Do you have a local butcher you can go to? Instinct or perhaps lore tells me you should have outstanding access to incredible brisket down-under but, I guess not.
That's a ridiculous state-of-affairs. I will keep looking for full brisket sources.
It's more of a cultural thing, different cuts are done in different countries. If you ask for a boston butt it's the same - they don't stock that, and never trained for it. I showed a chart to a butcher and he said the top shoulder is always separated but offered me pork neck which worked OK.
I think cows are big so a lot of places won't break down a full one and the briskets already come with the flap removed, last time I asked they said it wouldn't be simple to provide (I'm in a major city). So I tried the half brisket but it didn't have enough fat cap either, tasted OK but was too dry/tough. I'm sure there is one who can provide it somewhere, or by mail order.
That's a ridiculous state-of-affairs. I will keep looking for full brisket sources.