Any diode will work - use standard types like 1N4148.
Any 12V piezo buzzer will work - must be a BUZZER/SOUNDER not just a transducer. Buzzers have drive circuits built in.
Solder all points and wrap the diodes with the buzzer in strong tape leaving a hole for the sound output. Then just cable tie to wiring somewhere.
Total cost should be under $3.
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