Television producers love to set their shows in San Francisco and film them in places like L.A. or Canada. Typically, the only thing local about those productions is the obligatory bridge shot in the title credits. But the new HBO show “Looking” aims to be an exception, both in setting and substance. The series, which is shot in San Francisco and debuts on January 19, follows the lives of three gay men searching for love. We talk with creator Michael Lannan and three of the show’s stars.