Staples have a wide range of acid free paper and supplies? http://www.staples.com/acid+free+pa...free+paper
Also see http://www.universityproducts.com/ and http://www.gaylord.com/c/Preservation
A tip too is to be sure you keep those acid free folders in an air tight bag or box - such as zip top food quality or the paper will absorb acid and contaminants from the air? A desiccant pouch will keep any moisture down and a basic bug patch isn't a bad idea too.