You can only get those bulbs at the dealer. They are not a common part. You should be able to look at each one carefully to see if the filament is burned out, and/or verify with an ohmmeter.
You don't need to disassemble the control head to remove the bulbs. You just pop out the bezel which holds the control head, disconnect the wiring, turn the whole thing over and you can take the bulbs straight out the back of the unit by unscrewing them with a small screwdriver.

 

Thanks for the info!

I will try this approach since I have 3 extra bulbs from the old control unit and I know for sure at least one of the bulbs works.

Good point about the ohmmeter, should have thought of that too.