Bob's source:
https://spaenaur.com/catalog/L80/
We later found:
https://www.leevalley.com/en-ca/shop...es?item=A06508 but note that they say "no longer available".
Other sources:
https://www.mcmaster.com/hinges/hing...aterial~steel/ - often reluctant to ship out of USA
https://spep.com/product-category/pr...s/butt-hinges/ - may have minimum order size....
They seem to be referred to as "weld on butt hinges" in most suppliers' catalogues. Most seem to be square in overall dimension when laid flat but the originals were longer perpendicular to the pin than along it to allow a triangular rivet pattern. With the modern square hinges we had to accept a linear rivet pattern, offset a bit away from the pin to allow clearance for the thickened frame around the opening. Note also the pattern of the drillings to ensure the bucked end of the rivets don't interfere.