I know this is an old thread, but what the heck. This is what I used one each mounted across the indicator lamp in the guage cluster assembly on my ZR7.
View attachment 123613
Mini Buzzer 5-15V | Jaycar Electronics
it's not super loud (only 79dB) so you won't really hear it much at high speed, but perfectly loud enough when tootling around town in traffic which is where you really need it anyway and the current draw doesn't impinge on the effectiveness of the indicator lamps.
If you need something louder then use this
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Mini Piezo Buzzer 3-16V | Jaycar Electronics
90dB and you'll have people thinking a truck is reversing over them (again not waterproof, so also mount in the guage cluster).
Then finally a waterproof one like this could be an option, a bit larger and about 5 times more expensive, 85dB
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Weatherproof Buzzer 6-14VDC | Jaycar Electronics
In any case when mounting don't glue down the back as you'll muffle the sound, either screw down or use some hot glue or superglue at the mounting holes.
As for remembering to cancel the indicators, sure getting into the habit of cancelling after every turn and every lane change is essential, but when you're scooting around town and you have all manner of distractions to deal with it'll only take that one time where you forget to wind up putting you in hospital. Better safe than sorry in my opinion.
Cheers