Local OH company at one time Save Edge used to offer re-sharping of their files. Never checked into it though.Don't go snapping my vintage files! I get them re-sharpened. Usually better than factory, when I get them back.
I'm not sure how they do it, whether it's mechanical grinding or a chemical-etch process, but they come back damn near sharp as razors. Even the ones they mark as "reject" and don't charge me for, come back plenty sharp enough for my purposes.
I do recall they had more trouble with some of the older rasps, but it's honestly been enough years since I've had any re-sharpened, I forgot the what's and why's of all that.
Some guys swear buy putting their old worn clogged files into vinegar.
Loved their files till 2020 hit and they no longer offer square or round for chainsaw files. Raker files too.
Most of their blanks came from overseas. Then they did them in house here.
Just their rasp etc for others stuff still. Save Edge