See these threads:

Google Books: New source of music
Old Scottish songs at Google Book Search
Old Irish songs at Google Book Search
Songbooks: Old English songs at Google Book Search

The Forum search hasn't been working properly for a long time. New threads are not being indexed.

Here are some ways you can sometimes find things at Mudcat that the Forum search misses:

1. Use the thread title filter either on the main forum page
(http://www.mudcat.org/threads.cfm)
Or on the Discussion Forum Enhanced Search page
(http://www.mudcat.org/forumsearch.cfm)
Where it is called the Full Forum Filter.
(I sure wish this site would use consistent terminology.)

2. If you're searching for a song, try the message subject filter on the Discussion Forum Enhanced Search page.

3. Try a Google search of Mudcat by adding the term "site:mudcat.org" to any Google search. The Google toolbar is very convenient because it does this for you with the click of a button.