Okay, Calzone, Nokton48....
I happen to have a 5' length of 8" OD schedule 80 PVC pipe the contractors for the local water system gave me some years ago. I just checked and the ID is 7&5/8.
From what Calzone has said, that'd hold his 15' reels for 70mm.
If either of you wants some, let me know and I'll cut off a foot or so and ship it to you for postage if you want it. From what Cal said, that'd hold 4 of those 15 foot reels. It's got a 1/2 inch thick wall, so even though it's white, it's light proof.
You'd need to have somebody chuck the pipe in a lathe and square the ends, but Cal works at a company that might just have a lathe big enough to handle it. Failing that, I'm sure NYC has many machine shops that could do it. Get some end caps and figure out how to put a fill/drain plug in one of the caps and you've got it. (big laboratory stopper?)
Weight per foot is 8.05 pounds