Hi, Sandy-
I found it in a book called Young Folk Song Book, a Fireside book published by Simon & Schuster in 1963. It doesn't have any background information, but it does have a musical arrangement by Earl Robinson. Contact me by e-mail and we'll work out some way for you to get it.
We still could use more information on this song. Anybody know anything about its background?
Here's what Baez says about it in her Rare, Live & Classic box set:

When I was a teenager, I went to Trinidad with my boyfriend, Michael. His father had a record of Trios Los Paraguyos (sic*). This song was on their record. I fell in love with it immediately and spent that 17-day excursion working on it. Something inside me hears a song and says, "Sing that one." It's not very scientific.

Baez credits the song to "Hermanos Cantoral." Could it be that Baez is the only person who brought this song to the U.S.? The song was on her 1989 album, Diamonds and Rust in the Bullring. It's also on the earlier Vanguard album, Joan Baez.
-Joe Offer-
joe@mudcat.org

*Trios Los Paraguayos