There is a company, you may know of it, called Gesswein.
I went to gesswein.com yesterday - they have the standard files. They
have a die-sinker’s tool like a modern filing machine, but it takes
standard files. Somebody asked me personally about this, today, and
it made me wonder. I have MSC’s Big Book - 4" of machine tools, also
McMaster-Carr and a couple of others - machinery, not jewelry. No
non-tapered square files. American Pattern files have less taper, but
still some. Plus those are American pattern… But David’s right and
it made me remember - old filing machines used straight files of
various shapes. That’s one of those things that if you tried to
track them down you’ll get grungy old files for your year of looking,
though. Filing machines are pretty well gone from the mainstream, as
far as I know, and metal planers aren’t far behind them.