I don't know how I find $8 tires. But I do. I guess you just have to hunt, and wait for a deal. Just like the guys who score cheap/free bikes. And buy multiple tires if there is a shipping fee to make it worth it. Anyway you asked, that is how I do it. Amazon, jenson, treefort, sherpa, ebay, where ever they pop up.

I have scored 27's and 700's for the same price range as this screenshot.