This Australian term for a woman’s breast appeared in the early 1960s. The popular etymology concerning its origin was supplied by Sidney Baker in The Australian Language(1966), when he associated it with the NSW butter manufacturer, the Norco Co-operative—at one stage a cow’s udder was featured on the wrapping of the butter. This has never been a convincing story, and we marked our entry in The Australian National Dictionary‘of uncertain origin’. We received a letter from Fred Parkes who offers a different explanation:

By chance I came across the entry norks in your dictionary, saying it is Australian slang for women’s breasts, origin unknown. I can  set you right, having been around when the expression started. ‘NORKS’ is the abbreviation for the New Orleans Rhythm Kings—a famous band of the 1920s. They were frequently referred to as the NORKS by members of Len Barnard’s Famous Jazz Band in the 1950s (several recordings on the Australian Swaggie label). Somehow, a member of that band (and I don’t know which member) used the expression when referring to one of the dancer’s big tits, and the word seemed so appealing in that context that the whole band started referring to tits as norks. Within a short time the expression had spread throughout the Australian jazz scene and then gradually to the jazz followers among the general public. It originated in Melbourne, at the Mentone Lifesaving Club. The Len Barnard band had a regular Sunday night gig there for some years.... The expression was used in the band as a disguised way of drawing attention to big tits. After all, one could hardly call out ‘TITS’ from the bandstand to alert the other players.