All if not most of the tones heard on modern cars are computer generated. I don't think there is a soft bell type unit you can just screw in and put 12V to. Even the click you hear when indicating, is a computer generated tone, rather than a flasher unit clicking.
I put two buzzers on my coupe (bcause of the way the lights are wired) and one on my roadster. They make me jump the first time I use them after a while, but I no longer leave the indicators on by accident, and turn them off as soon as possible. I toned them down by wrapping them in tape.
Mart you didn't need two buzzers. Use two diodes from the buzzer to prevent the left side or right side from operating both sides. G.M.