I doubt you will find any that are willing to out themselves. Your best bet is to read and understand the law, or hire an attorney. Never get legal advice on the internet.
An AOW stamp is only $5 :)
Any Other Weapon (AOW) - Any National Firearms Act (NFA) firearm not otherwise categorized by the Bureau of Alcohol, Tobacco and Firearms as a short-barreled rifle, modern shoulder-stocked pistol, short-barreled shotgun, machine gun, sound suppressor (silencer), or...