Available Online Recordings for Acoustic Echo Identifiablity
I don't know of any online recordings, but you could try using the Silophone player to create some.  Play your original file, then record what the silophone plays back.
Silophone homepage

The Silophone uses an old grain silo as an echo chamber.  It also plays the echoed audio locally over a speaker outside the silo, so you might want to avoid using anything obnoxious or private or copyrighted.