You sound like Chicken Little warning us that the sky is falling. In actuality the sky has been falling on our gun rights since the bullsiht 1939 National Firearms Act.
Even though the UN may be able to somewhat affect the intercontinental sales of arms and ammo, there is absolutely nothing they can do on our sovereign soil.
Can you imagine the outcry if the government tried to shut down Colt or S&W? There is no way in hell that is going to happen, UN or no UN.