you can buy a 5xx slim from nicholson (they're about $3 each now). Bahco's files are super good, but they have a fairly round corner and they have part numbers for XX slim files and none that I've ever seen retailed. The fact that their files have a rounded corner and aren't available in XX makes them a bad candidate for small teeth - especially around 14 or a little finer.
The nicholson files are made in mex now, but you're sharpening a later saw and not cutting five sets of teeth in one, and could probably get five sharpenings out of a single $3 nicholson 5xx slim. The bad reputation for the mex nicholson was at the transition from the US to mexico when cooper sent their goods there, and now the files are probably about as good as the late american files, maybe minus 10%, but ...well, at least here, you can find ebay listings with new nicholson 5xx slim files for $3 each including shipping in packs of 5 or 6. That's more than 10% cheaper than they'd be if they were still domestic.
I do like bahco's the best, but they just don't make what you need until you're looking at needle files, and needle files for nearing $20 are really a waste of money for sharpening saws.