Over the past year and a half or so, ever since I moved five minutes away from the local flea market, I've been going over there regularly and picking up any decent-looking files I can find at a reasonable price (which for me is ~$1 apiece. Some folks think that their old rusty India-made file is worth a lot more 'cause "old file = super special knife steel!").
I've bought maybe two dozen files including maybe 5 or 6 Black Diamond Nicholsons and the same number of of miscellaneous Swiss-made, Heller, or Simmonds, with the bulk being plain old USA made Nicholsons. None of them are as new, of course, but at some point I'm going to go through them and pick out the best to send to J. Boggs, and anything that is too worn for restoration will go into the scrap steel bin and be recycled into something else.
Mr. Brooks is probably correct that you can build a gun with only a triangular and a flat file, if you are assembling a kit or stocking a rifle using all-bought parts. I wouldn't care to try building a rifle out of a barrel, a lock kit, a chunk of wood, and a couple sand-cast parts and sheet brass or forged iron mounts without a set of needle files at the least and preferably a half-round and a round file as well, though. And, of course, most of us do build stuff other than guns from time to time.