And if we ever again found ourselves in a war on American soil, Congress could certainly authorize private ownership of tanks and missiles.
But tanks and missiles as a protected 2nd amendment right? No court would agree to that, and the vast vast majority of American voters would disagree with it as well.
If (by fantasy), the Supreme Court found that the 2nd DID protect the right to own powerful war weapons, a new constitutional amendment could / would be passed in record time. The thought of private legal ownership of war weapons would tend to energize people.