Is there a super cover insurance we can buy on top of the collision damage free one? I see a deposit of $2990 is required?
Online normally you can but, NOT an Australian resident or a Kiwi.
So you have to take out insurance at the car rental desk on arrival. It is the rules of your two governments. They don't like there nationals being sold insurance outside your country of origin.
You will have lots of options, to view them in advance, look here:-
At STEP2 of our 3 step online booking process, to the right of the car photo of your choice, is a link entitled "IMPORTANT INFORMATION". Click on this link and it will open an additional smaller window, where the terms and conditions appertaining to that particular car at your chosen location are displayed.