Possibility #1: he has such fabulous sources in such quantity that he need not worry about burning a few dozen in every book he writes.
Possibility #2: he is either a member of or close buddies with persons assigned to Operation STARGATE, the remote-viewing program run by the CIA--the same folks who supposedly "remote-viewed" a "large, Saturn-like object" (was it the wagon or the sedan) behind the Hale-Bopp Comet.
Possibility #3: he's just repeating everything the little voices tell him.
Possibility #4: he's a BS artist.
I vote for #4, myself.