Making enough plutonium is pretty difficult from what I understand. In WW2 some of the biggest buildings ever built were necessary to house all the equipment to make just enough material for a few bombs (see http://en.wikipedia.org/wiki/K-25). Nowadays you need a nuclear reactor and fancy equipment like uranium centrifuges. See the Stuxnet worm and how it targeted Iran's uranium centrifuges in an attempt to disable their ability to make bomb material.
