Loc: Pensacola, Florida, USA
I was lucky enough to get the entire Wikifonia database of 6,675 lead sheets in mxl format. This is over 300 more songs than available on another site. (Wikifonia is no longer in existence.) The file is only about 35mb. Here is the link: http://www.synthzone.com/files/Wikifonia/Wikifonia.zip
You will need to download the free software Musescore to be able to view, transpose, edit, print pdf's etc. You will also be able to write your own songs with Musescore.
Loc: Lehigh Valley, Pa.
I batch converted over 6000 archived songs of the former Wikifonia Sheets to .PDF Format in alphabetical order, by song title. You can browse /search, and download individual sheets, or download two complete (very large) folders, The .PDF sheets are all in the default key of the creator.
Also, still available are the Wikifonia sheets .XML Format in alphabetical order, by song title, for editing in programs such as MuseScore (free)