Need some dead 8x10 film

I'm looking for a few sheets of 8x10 film, any type, exposed or not,
developed or not, expired or not. I want to experiment with cutting
it down to determine the proper size to fit all my recently-acquired
6.5x8.5 holders. I'm willing to pay postage if need be, but really
don't want to waste perfectly good film. I'm located just north of
Boston, MA, USA.

Or is there a standard size? I had one sheet that I cut to exactly
(well, pretty close) 6.5x8.5 but that was actually a bit large. Then
when I cut it down a bit it was obviously too small

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Thanks

Steve