Steve, I was surprised to hear that you couldn't get the "Sporting Equipment" allowance of an additional 10kg of hold luggage for free. I've checked again on the Air New Zealand web site and they still advertise the free "Sporting Equipment" allowance. I also checked with Air New Zealand staff at the Australian airport where I am based and they also confirmed the baggage allowance as I have previously described. As an ecconomy class pax on Air NZ you are entitled to a max of 20kg as part of your normal allowance & an adiitional 10kg of "Sporting Equipment" ( provided the item is obviously sporting equipment ie: golf clubs, gun case, etc) In total you can have 30Kg of hold luggage.
I also know that if you exceeded this limit you can expect excess baggage surchages to apply.
And just for the record I'm not an employee of NZ, and I generally travel QANTAS where I am a member of it's Club & Frequent Flyer programme. I only fly Air NZ when I go to NZ hunting as it's much easier to use the same carrier for International & Domestic Flights. And as I've said before I have always found them to be very helpfuly with the carriage of firearms.
I hope you manage to get your additional 10 kg of baggage allowance.
Rod