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.
Google occasionally turns up results if you search for names of specific filmstocks. 16mm is generally easier to source than 35mm. Even larger widths exist but are very rarely available for purchase.
Great for certain 126 cameras as well as medium format and large format roll backs but ironically impossible to use in 99% of 35mm cameras.
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