HP-45 power switch missing

[John Garza (3665)]

Most likely from a donor machine.
They were used on the Classic, Woodstock, and Spice series.
So the donor does not have to be another 45.
Buy a cheap 'for parts' machine and cannibalize it.

OTOH, you could try building one with a paperclip.
Ensure only the rounded metal touches the gold contacts on the PCB to prevent scratches.

-J