These are the ones I buy. I stick them on the back of the cardboard the stamps come on. I tape the stamp sheet onto the cardboard, and affix the magnetic sheet (these are cuttable in a TH guillotine trimmer, I have one dedicated to this and I keep several different sizes of magnets cut for getting sets ready and into my organization system) and then cut apart any dies, and set them onto the magnet, pop into a storage pocket which is already labeled, and poof - into the system in the right place, done.
https://www.amazon.com/Marietta-Magnetics-Magnetic-Sheets-Adhesive/dp/B01N25OLFS/ref=sr_1_4?crid=2G6OYV3DFFYGA&keywords=marietta+ma gnetics+5x7&qid=1579732101&sprefix=marietta+ma%2Ca ps%2C215&sr=8-4
Right now this pack of 50 is $26.22 and I get at least 2 and occasionally 4 or more from a sheet, and I don't ever throw a scrap away. So well worth the money and the adhesive is already on it!
I don't know why that's not hot-linking, grumble. It's Marietta Magnetics 50 sheet pack of 5x7 adhesive backed magnet sheets on Amazon. grrrrr.