They may already have a privately purchased crop duster sitting in a hidden hanger waiting for the order.
Or they may have twenty of them.
While I think we need to be diligent about fighting biological weapons (especially a mass production of smallpox vaccinations), everything I've read that sounds credible seems to suggest that isn't the case. There is a link (http://www.nov55.com/athr.html I don't feel like looking up the link command now) where the guy here claims that getting anthrax into the form where it is sprayed out in a crop duster is still technically hard to do. Still, it wouldn't bother me for crop dusters to be registered and have some sort of tracking on them so if they are near a city, they can be shot down or whatever if they don't get back on course...