Good luck on your pursuit of a die filer. I picked up an Oliver S-1 a couple of years ago off CL for $100. Spent over double that in die files since and have found it to be a very useful tool for my type of projects. I've used it as a "true" die filer a couple of times working a crazy-shaped punch to fit a die. Most of my projects involve working sheet metal, so instead of me working a needle file back and forth I let the tool do the work.
As mentioned by Eddy above, you can grind a regular file to file the filer. I've also read here where guys/gals have silver soldered a rod to the end of a file. Cut a slot in the rod to fit over the end of the file and silver solder or TIG in place.
Sorry about the arthritis, the golden years aren't always that golden . . . Plus side of retirement is more time to shop for stuff like die filers and spend more time in the shop! There are a few die filers on CL in your general area down below.
Bruce
https://sandiego.craigslist.org/esd/tls/d/milwaukee-die-filer-machine/6724482617.html
https://losangeles.craigslist.org/sfv/bfs/d/oliver-die-filer-filing-for/6735976134.html
https://sacramento.craigslist.org/tls/d/milwaukee-die-filer/6740642000.html