"I believe the 300 a day figure is just the M&P Shield line....doesn't include the others being produced."
could be true.
But according to the OP that ain't what the store clerk said. So the only part of what the clerk is supposed to have said that might be true is the number 300. That somewhere S&W produces about 300 somethings on any given day is the only thing that is close to true in what the clerk is reported to have said. Oh and maybe it's true that it's hard for his store to get guns from S&W these days. I wonder why?