I believe that we have signed and passed several nuclear limitation treaties, which according to article 6 of the Constitution, bare the same weight as the constitution, so it's constitutional to limit nukes. I do not, however, believe it's an issue worth any form of concern. A: we no longer produce nuclear weapons. B: the government doesn't sell surplus weapons of any kind, so even if we did produce them, the government wouldn't surplus them out. C: that would leave private companies to produce them which leads to D: they wouldn't, even if it was legal. So it's a non-issue. People can buy RPG's, but you don't see any company willing to make them and/or sell them.
Beyond that ridiculous attempt at an argument, no the 2A does not have limits on what type of weaponry one can own. If the government can, I can.