One doesn't, I don't think; I think one sells to one of several grey-market brokers who in turn sell to DOD. But I think it's more productive to substitute "the IC" for "NSA TAO", because there are several countries (on the "sort of legitimate" side of this market) buying. All of them can pull any plausible amount of cash for a vulnerability out of their couch cushions (then again, so can small countries).