I know what it is! I have them, I got them at a garage sale!
It's from Frank Schaffer's Teacher Club which doesn't exist anymore. Apparently, you joined and they sent you certain worksheets/ dividers every week. Seems kind of like an old fashioned version of Edhelper.
A lot of the worksheets are in Frank Schaffer's Best Buy Bargain Series. http://www.frankschaffer.com/
You could also try Ebay or Book Closeouts to see if you can find them cheaper.