Barry Popik's online etymology dictionary has a good history of use and early citations.

https://www.barrypopik.com/index.php/new_york_city/entry/rino_republican_in_name_only

> THe term “Republican in name only” was used in the 1920s and the 1950s, then in the Ronald Reagan-era 1980s. The term “RINO” appears in print in December 1992 in an article from Manchester, New Hampshire. In 1993, Los Angeles (CA) conservative activist Celeste Greig handed out “RINO” buttons to protest Richard Riordan, who was elected Los Angeles mayor from 1993-2001. It is not known if Greig coined the term “RINO,” but she helped popularize it.