So after not being successful in finding a reasonable priced Darkroom testprint maker I decided to design and print one myself. This is the result. Print both parts. In both parts are recesses for 8 small 9x2mm neodynium magnets. Place your photographic paper between the parts and stick it to your easel. With a small black piece of paper or plasticsheet(I just an old plastic A4 binder cut up to size) cover each slot except the one you want to be exposed. That's it! Hope you enjoy my design. Cheers!

Magnets: https://www.aliexpress.com/item/50pcs-9x2mm-neodymium-magnet-N35-Small-Disc-Round-Super-Strong-magnets-9x2-mm-Powerful-Rare-Earth/32953414476.html?spm=2114.search0104.3.28.484f362dJFligQ&ws_ab_test=searchweb0_0,searchweb201602_3_10065_10068_319_317_10696_453_10084_454_10083_433_10618_431_10304_10307_10820_10301_10821_537_536_10902_10843_10059_10884_10887_321_322_10103,searchweb201603_51,ppcSwitch_0&algo_expid=bfd7dd92-70e7-4679-aa14-d25d4c5fdb91-4&algo_pvid=bfd7dd92-70e7-4679-aa14-d25d4c5fdb91