Wilfried, you might search for "May morning," "first of May," and "month of May," all of which commonly occur in ballads and folksongs. Searching for these phrases using advanced search shouldn't get you in trouble.

What a wonderful idea you have had! I can't wait to browse it (but since I am at work, I will have to).

There's an English country dance tune called "the Twenty-Ninth of May," which is (I think, though the story is rather confusing) the day when Charles II was crowned king in 1660. In parts of England, people still commemorate the restoration of the monarchy by wearing sprigs of oak in memory of the time when the king hid from Cromwell's forces by climbing an oak tree following the Battle of Worcester. There MUST be songs...