As of November 2015, sources for line dance instruction sheets include websites for Steppin' Country, Kerry Kick and WGNA radio. Steppin' Country and Kerry Kick have alphabetical lists with dozens of links to step sheets. They also connect to instructional or demonstration videos for certain dances.
Kerry Kick's site lists the difficulty level for each dance. It also has links to additional step sheets and videos.
WGNA has links to instructions for several beginner line dances. Suggestions for appropriate accompanying songs match each dance title. For instance, The Darlin' Mambo is danceable to Kenny Chesney's "Pirate Flag," Taylor Swift's "Mean" or Lady Antebellum's "Downtown."