Not saying you can't get turned away by the border guards because they don't like the colour of your hair but the following are Homelands and ATF's actual official policies on the topic. Homeland makes reference to dealer but ATF makes no such distinction to non resident aliens. Again been down this road succesfully, not sure if I would chance it again based on how subjective these guys can be. Anyways
you don't need a form 6nia just bring solid proof it's antique and hope for the best.
From Homeland and Security website
https://help.cbp.gov/app/answers/de...rements-for-importing-new-or-antique-firearms
"If the firearm you intend to import is an antique and was manufactured in or before 1898, the dealer does not have to submit the Form 6 to ATF, however you must be able to prove to CBP that it was manufactured during that period. CBP will accept a certificate of authenticity or bill of sale with the year the firearm was manufactured as proof of age. If the firearm was manufactured after 1898, the dealer has to submit the Form 6 to ATF for approval to import the firearm.
If the firearm is at least 100 years old or more and you can provide proof of age, the firearm will be eligible for duty-free treatment under the antique provision in the Harmonized Tariff Schedule "
From ATF Guidebook of importation of Firearms
http://www.atf.gov/firearms/guides/importation-verification/how-to-use.html
"ATF Form 6 Parts I, II, 6NIA & 6A Exemptions
No approved ATF Form 6 is required to import any antique firearm, as that term is defined in the GCA
and the NFA. 27 CFR 578.115(c).
NOTE: you may need to supply proof to Customs to establish that a certain firearm, which is not
marked as being manufactured in or before 1898 is an antique firearm as defined in Federal law."
The reason for importation Roadking mentioned are reason for non resident alien to enter with a 6nia.
"1) Display at a gun show, you will need to have a letter from the event inviting you to come attend their event and bring such items.
2) Shooting event, this willl mean that the gun is capable of operating and this may raise other questions as to where are you get the ammo, powder ect."
Since an antique is exempt from all form 6 variants these reasons are irrelevant. Again not saying border agent won't think they are the only reasons, but honestly there are other legitimate reasons.
"At one time the BATF really didn't want to give any paperwork for bringing antique firearms into the country but now you should insist on it" I am curious what paperwork the ATF is providing as there is no official form for antiques or policy that states such documentation is required, and we all know the bureaucracy does crap all without an actual form. Could it be, the reason for their reluctance is because no existing policy, official ruling or federal law requires it, rather it's just to appease confused border agents? What do phone them up and say "I know neither US federal law, Homeland Security, Department of State or your agency's(ATF) policies require any documentation other than prove antiquity status to import an antique firearm but could you give me a letter so the half wit at the border is sufficiently obfuscated with your impressive letterhead"?