According to the Merriam Webster Dictionary, an op-ed is "An essay in a newspaper or magazine that gives the opinion of the writer and that is written by someone who is not employed by the newspaper or magazine" and stands for opposite editorial. Op-Eds are sometimes referred to as Opinions and/or Commentary.
Search for journal articles on most topics. This multi-disciplinary database is a good place to start if you don't know where else to begin. (EBSCO)