Assuming the latest version (.93b) typing rca in to the search window (magnifying glass usually at the top of the parts window) and hitting enter brings up 3 rca female jacks from core parts. Otherwise (and for things not in core) a google search on the lines of "frtizing part rca jack" often finds things not in the main repository where you can download and import an fzpz file for a part. The projects directory on the main fritzing site is another good source of user defined parts.
Peter