I was just about to buy PS plus and google found me this deal of 15 months for price of 12. It is a multicountry deal that includes Australia.
First deal posted so hope it helps some people.
PlayStation® Store only, excluding all other PlayStation® stores and in-game commerce.
15 month PlayStation®Plus membership for the price of the standard 12 month membership. The membership will continue indefinitely until cancelled and you will be billed in 12 month periods at the then current full PlayStation® Store price.
Further terms on link: