When I looked into it last year and called and emailed them, NZ customs were amenable to replicas of antique muzzleloaders (specifically OK-ing matchlocks and wheellocks based of the museum photos I sent them for reference), it was all the shipping companies that were the problem. I do not know the laws for muzzleloaders in NZ and if they need to be registered before shipping and similar nonsense. US customs also allows them, but if I remember correctly, someone on the pre flintlock forum was forced by US customs to have their muzzleloader delivery from Europe sent to an FFL, so who knows what actually gets enforced or made up.