One source (General Thoracic Surgery: Scientific Foundations and Clinical Practice, by Thomas W. Shields et al, 2004), claims it was created in this article:

# Patel AM, Trastek VF, Coles DT. Gossypibomas mimicking echinococcal cyst disease of the lung. Chest 1994;105:284–5.

This is the earliest I’ve found. Searches suggest it’s not as old as the 1970s.

The profession has coined a word for a left-behind surgical sponge: gossypiboma, from the Latin word gossypium for cotton and the Swahili boma for “place of concealment.”
—Denise Grady, “Forgotten Surgical Tools ‘Uncommon but Dangerous’,” The New York Times, January 21, 2003