It's available at the Zawadi Marketplace (the gift shop in Jambo House), but I'm not sure if it would still be open by the time you get to AKL from the airport. I'd probably just wait until you enter the park the next morning.
Thanks for the helpful information. It would be nice if it is still open! One less thing to do at rope drop in the AM. But now I know where to go looking once we arrive. Thank you.