Hi
Bit late on the die filler, not sure you know about Vintage Machinery site, http://www.vintagemachinery.org/home.aspx. It has lots of information on many companies like Keller. Not sure which model you have, here is link to Keller 1A model manual: http://www.vintagemachinery.org/pubs/detail.aspx?id=23070
I have an All American die filler here is a link to it : https://www.owwm.org/viewtopic.php?f=77&t=179474
I use mine a lot and have a nice collection of files, I find them at flea markets, you need to look carefully but a giveaway is the tang and that there is no taper on any sides, as well as the direction of the cut when you drag it across your fingernail. I have made adapters for short files to fit my machine.
Bob
Good advice on finding machine files, I've made a few now & am getting better @ making them, its not overly hard to do & donor files are easy to come by/buy 😊