Nothing wrong with asking. The response you got seems a little short sighted for a guy who sells cues. My guess is a miscommunication. Maybe what he thought he heard was you asking him to tell you who the buyer was and did not fully understand what you were actually asking him to do.
Or the guy is just goofy and doesn't understand how to keep a dwindling customer base interested in what he sells.
EDIT: It always does kind of amuse me how some guys treat cue deals like nuclear secrets though. I suspect its often done so as not to spook the fish.