Oh, I don't know. Perhaps the same place they found authorization to run a multi-billion dollar air force? What -- you mean there's no air force clause in Article I, Section 8, but only a reference to "land and naval forces?" Begone, USAF!!!! Begone ballistic missile defense. Begone ICBM capabilities!!!!
(PS: I think one would place such things under the "common Defence and general Welfare of the United States" clause.)
Do you have any doubt that we would easily amend the Constitution to add authority for the Air Force...or missile defense?
Neither do I...but it seems that the attitude by 1947 was, why amend the Constitution when we can just ignore it?
Unfortunately, that is the preamble. We would call it the mission statement today. Everything intended to accomplish the desires spelled out in the preamble are contained in the articles of the Constitution. If you can't point to an article for justification, then it ain't in there.
This is a pet peeve of mine, because it's the same justification that liberals use for Welfare. "The Constitution says 'promote the general welfare,' so direct payments from the treasury are what the founders intended. "