Don’t call Peter B. DuPré a musician. That’s not how the 96-year-old World War II veteran would describe himself. “I am a harmonica player,” DuPré, who spent three years stationed in England as a U.S.

About 500 harmonica players have descended onto the San Antonio River Walk for a convention with a single purpose: preserve and promote the fading use of harmonica in popular music. Harmonica ...