Need help with the name of an interior part
 

I am missing the knob or lock that closes the First Aid Kit door in the back driver's side of my 2008 R350. It looks like a plastic flat screw that you would open with a quarter. Can someone tell me what the name of this part might be? And if you could suggest where to find one (outside a dealership) that would also be very helpful. Much appreciated. Love this forum!