The breasts, worth £100,000, were planned to be a free gift in Ralph magazine - but vanished before arriving at their destination.
A spokeswoman said the container left docks in Beijing two weeks ago but turned up empty in Sydney this week.
The magazine has put out an alert to shipping authorities but the breasts need to turn up in the next 48 hours to make the January issue.
Ralph editor Santi Pintado urged anyone with information to contact the magazine, saying: "Unless Somali pirates have stolen them it's difficult to explain where they are.