where can I buy a replacement switch?

The CDR500 in my wifes car seems to have a faulty on/off/volume switch as the unit comes on by itself when driving or even when the car is not being used, and is often on all night.

The system is not wired through the ignition or this would not be a problem.

I can get to the switch itself but where do I buy a new one please??

Hacked off husband.
January 2009