Ben Eadie, props guy on GB:A has a Tiktok. On that Tiktok he mentions this very switch in
this very video.
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The writing at the top looks like HEINEMMAN ELECTRICAL to me, which does indeed manufacture breaker switches. There is no visible part number in that switch but there are some very specific specs noted. That said, I don't think the specs matter since the breaker isn't used as a circuit breaker on the pack.
I think you could use any Heinemann circuit breaker that looks right and turn it into a switch.
This one, just as an example:
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I'm not sure what Ben means about the light switch he mentions in the video. I'm not certain if he's saying a light switch was cut down to look like the breaker switch, or if he means that the light switch was positioned under the breaker.