Green’s Dictionary of Slang

(US) the breasts.

1987		‘Joe Bob Briggs’ Joe Bob Goes to the Drive-In 10: The immortal Herschell Gordon Lewis [...] who put nekkid garbonzas on the drive-in screen for the first time in 1959.
1999		B. Kelly A Century of Hollywood Murders 🌐 From the time Sennett’s top comedian, Rosco ‘Fatty’ Arbuckle, feasted his roving eye on Virginia’s bulging garbonzas, he wanted her despite the fact that she had been around more than a carousel.
2003		Canyon News 1 Nov. 🌐 She begins to kick his ass and knock him to the floor, only to pummel him with a left-right combo of tatas and garbonzas.