In the author's photograph on the dust jacket of the 1972 novel "The Stones of Summer," Dow Mossman is lean and rangy with a defiant mustache and a look of conviction. The producer and director Mark Moskowitz has, by comparison, friendlier facial hair but an ingratiating and determined manner: he's going to find Mr. Mossman. It's what his film "Stone Reader" is all about: the director's search for a writer whose single work is still a touchstone in his life.