i dunno where you'd buy a kit or anthing but it wouldn't be hard to make n.e way.
you'll need:
- buzzer unit
- fuse
- relay
- about 5 meteres cabling (if u mount the buzzer in the cockpit)
just run a positive wire from the battery (through fuse to suit buzzer) to the relay, then run a positive wire from the relay to the low beam positive.
now run a wire from the door positive wire on the room light to the switch terminal on the relay.
you'll need to explain to an electrician what you're doing to find out what relay you'll need.