According to Eric Partridge’s A Dictionary of Slang and Unconventional English (1961), the following meanings are listed under gay:
* Gay boy. A homosexual: Australian: since ca. 1925.
* Gay girl; gay woman. A prostitute.
*A dupe: Australian.
Now, it’s not entirely clear whether this sense of ‘gay’ was coined in Australia, or whether ‘gay’ = Australian.