Ok from what I've been told it's had to find an original voltmeter switch so I think I came up with a substitute. I took a Cole-Hersee 9055 momentary door switch and modified it a little and it looks pretty close. The switch is on with the button out so that's where the modification comes in:

Use a 9055 Cole-Hersee Momentary door switch

Pry the little tangs back and take off the lid. Keep it up right or all the little springs come out. Turn the lid 180' and reinstall lid. The switch will now be normally open and closed when pushed in.

Ready to install

Sheezam, almost looks original. Sorry for it being upside down but that's the way my dash is right now. I found the switch on ebay for about $5.00. I put power to it and it works great and looks like an old timey switch to boot. Hope this helps!
Don G.