Terence N. D'Altroy reports that the Incas had slings as part of their weaponry.
Terence N. D'Altroy, The Incas, 2nd ed. (London: Blackwell, 2015), 345
The Inca battle formation was organized by ethnic group, each one of which specialized in its own arms (Mena 1937: 83; Cabello Valboa 1951: 308; Cobo 1990: 218; Rowe 1946: 276–7). Flurries of arrows, sling stones, and javelins preceded hand-to-hand combat by troops who wielded maces, clubs, and spears.