Where to Buy

//www.metroinfo.co.nz
Metrocard is not available for purchase on buses, but you can purchase and top up your card at any of the below locations:

Bring ID with you as staff must sight it to issue a card, accepted identifications are – drivers license, birth certificate, passport, Cando Cards or School Identification with your name and date of birth on it.

>運転手さんなどから購入できるのであればすぐに購入したいのですが……。

残念ながら不可ですね。
Christchurch
空港はないですね・・・。

Metrocard FAQS
More than one person on one card

You can take other people on your card, but you will be charged a full cash fare ($3.50 Adult, $1.80 Child fare), so it is cheaper for each person to have a card. This cash fare will provide only one free transfer within 2 hours.

これで決心が付いたでしょう・・・。