The list still says 82.55mm for 122, though. Please double-check the size before actually cutting the stuff. 92mm is closer (I just measured it again).
I also note the availability of backing paper, but it only seems to come in 120 size. Could this be made available in wider widths? 122 would be great, but wider even than that would be even better for me, because there are a few cameras in my basement that use even wider stock than that (123, 126, even 104, although the latter isn't working at the moment). I suppose I could slit it to 1-3/8" wide and tape it to the side of another piece to get 3-5/8, but I'd be afraid of light getting in through the crack if I don't line it up exactly right.