Nicholas,
I checked through my collection of saw nuts and also checked my Disston saws that range from late 1800s thru WWII era. They are all the same dia, close to .210
What you have must be of the older split nut type.
They generaly do not survive removal as many bradded the end of the threads to tighten the handle. If you should find a source for these please let me know.
I had the same problem with an older saw, but as I wanted it for a user, I simply took a small round file and opened up the holes to acomadate the later type nuts.
Should you decide use this method. I learned to size the first hole and put it on the saw, lightly clamp the handle and work the others with it attached to ensure proper location.
Regardless its a good find.
Lamar