Not sure if it's exactly what you're looking for but there is some old stuff at
http://neatopotato.net/xnovel/browse_series They seem to be text files (some with a jpeg of the original cover) but with a program like sigil you could easily make your own epubs from that. I'm assuming they either aren't under copyright or that the publishers/authors let the copyrights lapse since they are free to download by all appearances.