Believe me, Kino, with the price 620 spools are fetching on eBay these days, I have seriously considered fabricating a bunch of them. Hobby brass tube and sheet, and a little jig to let me true up center drilled, rough cut end flanges on my lathe, two minutes with a torch and solder at each end, and another two minutes with a fine file, plus one minute with a Dremel -- if I could be sure of selling 'em for $10 each as sometimes happens on eBay, I'd start production tomorrow; I could probably turn out 50 of 'em in a week without eating into my photography time.
In a lot of ways, 127 and 828 spools are simpler, because they don't need a slot in the flange; nor does the little ratchet on the end actually need to be slanted; a single slot in the tube would work just as well to engage the drive on every 127 or 828 camera I can recall examining.
For backing paper, there's a material out there that's very suitable; it's called, IIRC, Exeter Paper; it's black, opaque, only slightly heavier than modern commercial backing paper, comes in rolls a foot wide, and one side is glossy (to protect the film) while the other side is plain (to take ink well). Find an ink that's visible against black and won't "wrapper offset" (fog the film from contact with the ink), and you coul d make backing for any paper backed format ever produced. Then it's just a matter of getting film wide enough to cut down for formats like 124 (3 3/4 wide, took eight 3 1/4 x 4 1/4 frame) and 125 (4 1/2 inches wide, 4x5 frames, IIRC 6 on a roll).
For now, though, I'll experiment with 127 and 828 -- 120 is easy to get and conveniently includes a backing roll...
BTW, Dave, I meant to use the 120 backing, not to discard it; I was just saying you don't need an original 127 backing to reload...