I couldn't help myself.... I hadda go look: Sandburg heard the song from the cartoonist, journalist & "philosopher," John T. McCutcheon (you've seen his stuff, likely - worked a lot with George Ade)

And he has: (I just asked inter-library loan for one but there's plenty of copies. {8})

Title: The island song book : being a small collection of our favorite ballads, anthems, lullabies and dirges of this particular section of the Bahama Islands and also such other ditties as have seemed befitting by reason of their piratical, nautical or sentimental appeal. Together with several local and topical lays relating only to Treasure Island. To which is prefix'd an explanatory and historical introduction. To which is added a number of sketches and photographs illustrative of same.

Author(s): McCutcheon, John T.; 1870-1949. ; (John Tinney), Evelyn Shaw. ;

Publication: Chicago; Privately printed at The Chicago Tribune tower; 1927