Jaycar will sell buzzer. Search BUZZER on their site...
Heres 2 from their site you could use.
"AB3452 RRP $3.95*
This handy little solid state buzzer operates between 5- 15VDC.
Used in many applications"
"AB3462 RRP $3.95*
It offers medium to loud sound output, low current consumption and is extremely durable."