Of course there is the Broadway show "Barum" which has several circus songs including "join the circus".    I also think of Tears of a Clown by Smokey.   Richard Thompson has one about a high wire person named "valerio"   (not sure about the spelling)   There is the Peter Allen song "Don't cry out loud" which starts "baby cried the day the circus came to town" and has a lot of other circus references.