If you have looked at the various datasheets, I am out of ideas for an exact match. Well, you could/should try HP if you haven't already.
I can suggest two ways of using a switch with the incorrect spacing. First you can buy one that will physically fit and bend and/or extend the pins. You may need to find one that is shorter in height if it is a tight fit in the available space. The pins can be cut fairly close to the bottom of the switch, leaving only the diameter of some buss wire protruding. With the buss wire laying flat on the bottom of the switch, bend it around the terminal and solder it in place. Once the solder joint is good, clip the terminal flush with the buss wire. Finally bend the buss wire to create a new pin at the needed location. Then you will have added only the diameter of the buss wire to the height of the switch.
A second way would be to drill new holes or file the existing ones into slots, but keeping as much of the foil pads as possible. The pins of the new switch can be bent over after inserting it in the new hole pattern to give them good contact area with the remaining foil. Not the best way if you like your vintage electronics as pristine as possible, but it will work.
As for that ruler, other then the scales themselves, the only markings on it are:
ENGINEER
Alumicolor
Code 3211
and Made in El Salvador
I do not remember where I purchased it, but when I searched for an Engineer rule Code 3211 I was surprised to come up with this:
https://www.amazon.com/Alumicolor-3211-1-Aluminum-Engineer-Pocket/dp/B004BNHA5AThat seems to be the exact one and I often buy from Amazon. They have different colors now and I may buy another one or two. I also had other hits. Here's one:
https://www.engineersupply.com/Alumicolor-3211-1-6-Engineer-Pocket-Scale-with-Clip.aspx?VariantId=87fcc7b3-5fba-474f-a6cf-299e234a44e4&gclid=Cj0KCQiA4OybBhCzARIsAIcfn9kymEsqi3JT_N2sXGr4K-4trfBSEVkN00hvtk4--tFx4EmvSBiHMNsaAgK2EALw_wcBAnd a bunch more. My search was:
https://www.google.com/search?client=firefox-b-1-d&q=Engineer+ruler+Code+3211I measured it with the caliper, the short side is 0.25 inch (center to center) and the long side's pitch is 0.275 inch (center to center). Before asking here, I already tried getting the datasheet for each brand in the search results from mouser and digikey (actually there are only a few distinct datasheets there), and I couldn't find anything that has this exact pin spacing. The closest ones I could find have 0.25 inch for both long and short side. If the long/short sides are slightly different, it's the short side that has the wider pitch, which is the opposite of this one. I also searched TE (Amp) and they do not have parametric search by pin pitches either. There are only 30 DPDT switches anyway but none of them have this pitch spacing pattern.
Good idea about getting a ruler with finer graduations. Is there a name for it? It'd be useful for taking pictures as a reference. Caliper often gets in the way for photos.