Gypsy - You can find the sheet music in Mrs. J. Luis Baños: Collection of Latin American Sheet Music, 1908 - 1921; 1931 at The Latin American Library, Univ. of Tulane, wherever that may be.
"The Latin American Library, located on the fourth floor of Tulane's Howard-Tilton Memorial Library, is one of the world's foremost collections of source materials in Latin American archaeology, anthropology, history, linguistics, art, architecture, film, women's studies, economics and many other subject areas."

To buy from
GUITAR GALLERY MUSIC CATALOG Click to Order 564010960
or (for harp) Melody's Traditional Music & Harp Shoppe

More to be found searching Google with "las gaviotas" "sheet music" (quotation marks essential).

Ejoy your strings
Wilfried