To me it looks too ordinary and oddly specific to be custom made. It's gotta be some breaker switch or something from a piece of equipment that somebody had laying around. I would think the bump on the side would be either for surface area if someone was wearing gloves or so that a switch next to it would get tripped.
if you watch Adam Savage build his own proton pack video... he has help building his pack from people from the new production, but still fabricates his own switch. I would imagine they would have the answer as to what switch and where to acquire it. Id bet its fabricated