Yesterday, I was helping a friend who attends a nearby smaller lay-led Unitarian Universalist fellowship find prerecorded instrumental music to accompany congregational singing.
Many of the familiar Unitarian Universalist hymns are also available on audio CD for use in congregational singing, and she has used these resources before (a useful listing of what is available can be found online on the Church of the Larger Fellowship web site).
However, she couldn't find any music to accompany "Here We Have Gathered" (#360 in Singing the Living Tradition). The melody for this hymn is called "Old 124th" in the hymnal. That indicates that it's a traditional hymn melody and probably in the public domain ("Turn back, O man, forswear thy foolish ways" as I discovered later).
We did a quick Google search for "hymn mp3" and found "smallchurchmusic.com" -- an online archive of music Resources for congregational and small group singing (mp3 files, midi files, PDF scores, and lyrics available. The public domain music on their web site can be downloaded freely. The copyright-protected music requires a small fee for use. According to this web site, there are 2560 public domain mp3 files available for download on it.
So ... a quick download of the "Old 124th" mp3 audio file and then burning it to audio CD will now mean that a small lay-led congregation that has lost its pianist will be able to sing "Here We Have Gathered" with organ accompaniment.