For retail purchase, h.sapiens gave you good advice. Photo background paper is certainly wide enough (but maybe not 80 continuous feet long). It comes in a rainbow of colors. I know that a company called Savage is one manufacturer.
bidee’s suggestion is good too. Web printing presses use giant – and I mean giant – rolls of paper (a roll is called a “web”). Web presses are used to print large print runs like newspapers and some magazines.
They do not stop the presses between webs; they glue the end of the expired roll to the front of the new one using a mechanism called a “flying paster.” As you might imagine, this is not exactly microsurgery – it is a speedy and wasteful process that results in lots of almost-but-not-quite empty rolls of paper that the printer considers waste product.
These “web cores,” as they are called in the trade, are what you want. They usually contain many, many feet of perfectly good paper that is, oh, about 5 or 6 feet wide. You can probably have as many as you can carry from a friendly printing plant. The trick, of course, is finding a place that won’t tell you to stop wasting their valuable time with your stupid girly craft projects. Printers tend to be no-nonsense tough guys.