When I've made up 828 for my Bantam RF, I've cut a 35 mm wide strip from the 6x4.5 track edge of a 120 roll. After trimming the paper leaders to roughly half length, this will (barely) fit between the flanges of an 828 spool, and give sixteen exposures with a little extra space between when you us the red window -- or, if you have a friction roller advance stop like the Bantam RF, you'll get 18 frames.
This gives you access to any emulsion you can find in 120.