A Harlem restaurant-supply store owner unleashed a round of shotgun blasts on a gang of four robbers Thursday afternoon, killing two of them, police said. The shooting happened at about 3:10 p.m. at The Kaplan Brothers’ Blue Flame, at 523 West 125th Street, near Amsterdam Avenue, according to cops. One man died at the scene and the another died at St. Luke’s Hospital. Residents said they were surprised at the robbery the store is not known as a cash business. Detectives are still investigating.