I saw a couple of these on Etsy, but no one was willing to sell just the files, so I made my own version. The advantage of my model is that you can print more “guides” to fit the exact gap for each caliber. I have created models for .223 Rem and .308 Win, but its very easy to make new ones.
You need some magnets to attach to the trimmer:
6mm round magnet (3mm tall) for each guide
2 x 8mm round magnet (5mm tall) for the catch bin
The author marked this model as their own original creation.