Ditch lily is just a common name for Hemerocallis fulva, or common daylily (not a true lily). It is a naturalized form - tough, hardy and considered invasive in some areas. Any other form of daylily will work equally as well, as they all share a very dense and fiberous, spreading root system.

And online daylily vendors are almost too numerous to mention :-)) You might get more specific advice from the Daylily forum.