Have you read Ryan Mauro's website? You just described it.
No, I haven't read it but I could have figured as much.
There is a limited amount of nuclear weapons, components, and fissle material on the market. Rogue states are also trying to get ahold of these materials and anyone having this stuff for sale would have a far easier time contacting an agent for a rogue nation than AQ. I would say this story is probably bogus because N. Korea or some other state would swoop on the stuff and eliminate any sand-nazis trying to muscle in. It is possible the terrorists have nukes and wmds (of course), but they probably would already have tried to use them if they had them. Why fly planes into bldgs if you have a far bigger firecracker? The maintenance on nukes and danger of contamination is high and chem and bio wmds are equally hazardous to a potential user without considerable expertise. This explains why there have not been too many wmd terror attacks already. Many of these wmd materials are also rather easily detected.