The chest buttons on my robot will be genuine, functional push buttons, and I have purchased the necessary supplies to achieve this goal. Thanks to the handy information on the internet,  finding these parts was simple. They consist of a switch, what must be the worlds' smallest incandescent light bulb, and a switch cap. As you can see from master B9 builder Mike Joyce's website (see the journal entry for 25 February 2001), these are mounted on a specially machined plate behind the chest buttons.

I ordered the parts from Allied Electronics, Inc