Readers took their time finding Kent Haruf, but he was a patient man who didn’t care much for the trappings of fame anyhow. His popularity swelled quickly, though, when he published his third novel, “Plainsong,” in 1999 at the age of 56. The book was a bestseller for months and a finalist for the National Book Award, which meant he had to dress up for the ceremony in New York and wear a medal on a ribbon around his neck and feel genuinely uncomfortable.