As far as i can see there are no travel prepaid cards available to buy in the UK in A$.

Its certainly not worth getting a euro or dollar one as you will end up paying exchange rates twice (pounds to euro/$ and then into A$).

The best card would be a nationwide credit or debit card. they charge no commision and offer one of the best exchange rates (i check when i go through my statments after holiodays). The debit cards also free for using in foreign ATM's! If getting an account with them is too much hassle, then just apply online for their credit card and make commision fee purchases when you're there, you then only need to bring enough cash for taxis etc where you cant pay by card.

Hope this helps