When I owned an MG Midget many years ago, the horn failed a few months after purchase (Lucas). I replaced it with a set of Fiamm air horns. Sounded like a Semi truck. For a little car that people thought was OK to pull out in front of me or attempt to swerve into my lane, it would scare the hell out of them. it came with a small air compressor, I believe they are still available.

Wayne