This is the very last place I know of. http://www.jdlacourseandson.com/
Older than the hills...

We use a 120 tooth thin profile blade to cut chrome plated alumnium without chipping the heck out of it, and it costs in the $300 range, so it's worth having it set and filed....

The $12 Home depot blades just go in the trash tho...sigh

Here in Sacramento, I miss Buletti's sharpening shop.  It's wooden floors smelled of three generations of machine oil.  I had everything sharpened there, from dovetail saws to adzes and draw knives.  They did great work on everything.  But we still have a hand sharpening business -- Nobile's Saw Works.   Smells right.  Looks right.  The old man has turned it over to his son mostly, and his son is no spring chicken.

I'm unpacking tool boxes now,  and I'm glad to report I have quite a few saw files, including a few old Nicholsons still in the box I bought 30 years ago.  I'm set for a while yet.  It's really sad to hear about the loss of quality from Nicholson!  And more than a little disgusting.

My friend, Colin Dipper, makes concertinas by hand. The reeds are made from pretty hard spring temper steel (best silver steel as used for saw blades and wood scrapers) - he wears out a file to make a set of reeds (2 per button, most concertinas have at least 30 buttons). He is finding it more and more difficult to get files... extra slim double tapered saw files are his favourite.... good quality ones are like hen's teeth in the UK... he can find them, but most are not hard enough (one by Draper was so soft that he was able to cut the end off with a junior hacksaw).

I note the Nicholson files (link above) are made in Switzerland (they are probably Vallorbe) - and they are not double ended, so he would need at least 2 per instrument....