Buy NZ Made is a good resource;
https://www.buynz.org.nz/

+1 for Cactus Clothing. It's expensive but they guarantee it for a lifetime and handle repairs.

Some companies I haven't seen mentioned yet;

Mussel Inn micro-brewery, not sure if their brews are available retail but they're great!
https://www.musselinn.co.nz/Brewery/brewery.html

https://www.musselinn.co.nz/Brewery/brewery.html

Ocho chocolate factory in Ōtepoti;
https://ocho.co.nz/

Baker Boys biscuits, based in Ōtautahi;
https://www.bakerboys.co.nz/

Last Footwear Company, reputed to be the Cactus of shoes. Can't find a homepage but they're on FarceBook.

Haka Clothing is a maybe;
https://www.hakaclothing.com/about-us

They say it's designed and hand-printed in Aotearoa, but they don't specificy where it's made. But someone gave me a Haka hat as a present and it lasted about 15 years in heavy use, so ...