Hammond native Nick Mantis knew little about humorist and radio legend Jean Shepherd until after the city hired him five years ago to produce a short tribute that commemorated the 25th anniversary of "A Christmas Story," Shep's best known and most enduring work. The television veteran, who owns New Millennium Productions and had produced the "Around the Region" cable show, first started listening to Jean Shepherd's old radio shows early last year when he was zooming east on the Indiana Toll Road toward a Jean Shepherd tribute at the Paley Center for Media in New York City. . .