There's some government agency, the AFT I believe, that publish an annual report on the number gun's sold by Company. They break it down into semi-autos and revolvers. Something about chamberings (caliber). But no more detail than that.
I think the M642 would be a good guess on most produced current S&W revolver. What would be next, or close, that new plastic 38 Bodyguard thing? The robots can spit them out like Oscar Mayer hot dogs.