Bringing stuff into NZ is the easy part, if it's on the approved list your sweet..... getting it out of the US is the tricky part.
Firearms Approved for Use in New Zealand. | New Zealand Police
The yanks are paranoid of sending out gun parts, mazagines and rifles etc.
Each state has it's own set of rules and what might be ok in one state may not be ok in another even if your in transit.
You will have to brush up on the laws exporting concerning firearms and firearm parts.
These sites may help answer some of your questions.
GunBroker.com - Help Center
World's Largest Supplier of Firearm Accessories, Gun Parts and Gunsmithing Tools - BROWNELLS
That said I had a mate bring back two 10 shot magazines for a .22 Armi Jager AP74 without any hassels.
None of the sites that sold them would export because of all the paperwork involved.
But if you really want to bring something back I could do with one of these for a small job I have to do
.22 CHAMBER IRONING TOOL - Brownells
Cheers
Pete
Bookmarks