It is still legal in New Zealand to own and trade Ar15s, although importation of new Military Style Semi Automatics (MSSAa AKA assault weapons) has been banned since 1989. Those still in the country can be legally traded if the buyer has the appropriate firearms license - the Police don't give these out anymore without a very good reason. The present left wing government have had one go at tightenening the firearms laws, including compulsory buy-back of certain firearms, but backed off when the cost became public. They had another go at grandfathering them ( i.e. present owners can't sell, must hand into police without compensation) but dropped the idea when not even the antis supported it.
However, it is only a matter of time, there is an election at the end of next year, and I predict that right after that, knock knock at 6am one Sunday morning, you can imagine the rest.
Anyone in the USA got a vacancy for a middle aged IBM Mainframe techical consultant? (Joke)