I know that there are better sources for typewriter ribbons than my local office supply big-box store.
Jay Respler has his share of business from around the Typosphere, and I've seen Baco Ribbon & Supply mentioned a few times. With my general budget-mindedness, though, I usually opt to roam the printer ribbon section at Staples. They sell 2-inch diameter plastic spools of 1/2-inch wide nylon "printer ribbon" that is meant for a dot-matrix printer. I figure that application is pretty close to that of a typewriter -- short impacts -- and for NaNoWriMo, I'm not as picky about quality.*
The above photo is the three different packaging variations I've seen over the years, from oldest on the left, to the current supply on the right. The common theme is that they are meant for a line of Okidata printers, in models 80, 82, 82A, 83, 83A, 92, 93, "and others." Also, evidently, the Xerox Phaser 3300.
The spools are nothing special, but the ribbons have the familiar grommet near the end to trip the typical portable reverse mechanism, and are drop-in replacements for many of my portables. The ribbon is all-black, and 12 yards long. They're fairly durable, and I've re-inked them with success.**
These are not the "Universal Typewriter Ribbons" which have the evil strip of flaky, useless "correcting" material on them. I avoid those like a pile of fresh rhino poo, as should you.
* I suspect the cheap ribbons are part of the reason why I have such issues with OCR, since they leave a fine dot pattern inside open letters that sometimes trips up the software. A larger issue for OCR, though, is my bad habit of backing up and over-typing my mistakes. No ribbon is going to fix that.
** Also, with ink. And WD-40. Unlike the delicate re-inking procedures I've seen other folks use, I just drip black ink into the wound-up ribbon, zap it with WD-40 to theoretically spread the ink around (it's a solvent of sorts, right?) and then let it all sit in a sealed plastic bad for a while. The end result is not bad, although sometimes you get
bold blotches in your typin
g where you hit damp spo
ts in the ribbon. Again, it's NaNoWriMo, so my tendency to care about this drops off noticeably.