Three words...Abdul Qadeer Khan.
A rare genius. A one man show.
...who sold some things to Iran and Libya and North Korea (none of whom have demonstrated a single working nuke), but not to Al Qaeda.
Even if you believe that Iran or North Korea would give working nukes to Al Qaeda...one must first have such weapons in order to give them away.
You do realize that we are boarding every North Korean ship, yes?! You do realize that we are monitoring for a nuclear test, yes?! You do realize that we are engaging Iran this very moment in order to short-circuit their attempt at acquiring this technology, yes?!
And stopping this problem at the state level negates any chance that Al Qaeda would have at obtaining such weapons.