Well, then the threat of use would have to apply. But since the use would ultimately negate the effect and purpose of having them.
But this is all pretty pointless. Even if they were legal to own, you'd have to find someone who wanted to sell you one and since they aren't being produced anymore, that'd be mighty difficult. And if someone happens to know already, and has the money, then there isn't too much to stop them at current anyways. So in every way, shape, and form, it's a non-issue and distracts from ACTUAL concerns.