i don't know the details, but i have a friend who imports antique guns from NZ regularly. once the initial paperwork is done it seems like it is quite easy
talked to my friend and he says antique is pre 1899. if it is that old the job become much easier. Post 1899 require a bit more paper work. customs here or there should be able to answer a bunch of questions. you must have an importer here, who handles the papers. freight is expensive but there is not to much for other fees, providing it is pre 1899 and a shotgun. rifles and pistols are much harder i believe the crux is to find the importer
talked to friend this morning - providing the gun is pre 1899 he doesn't need an importer. the recipient here goes to customs & fills out a couple forms, the gun is shipped via customs, when it gets here customs looks it over the he can claim it himself