If your research paper includes a source that you cannot locate, you may have no choice but to reference it as discussed in a secondary source. When citing a reference within a reference in American Psychological Association style, the rules are different for an in-text citation versus a citation on a references list.
References List and In-Text Citations
If you are citing a source quoted within another source, only the secondary source is included on your references list. There is no need to note that you are quoting a source within the source as part of this reference.
When citing quoted material in the body of your text, mention the original source in the sentence and the secondary source in a parenthetical citation at the end of the line. For example:
Lévi-Strauss' discussion of the transition from animal to man hinges on principles of exchange (as cited in Bataille, 1989, p. 39).