This AH:SW Selected Sermon set contains Augustine's homilies on the Gospel of John and only one homily on 1 John (chapter 1), Augustine's remanning 9 homilies on 1 John can be found in NPNF Series 1, Volume 7. Available here: https://ccel.org/ccel/schaff/npnf107.toc.html as well as on logos in the ECF bundle: Nicene and Post-Nicene Fathers, First Series, vol. 7: St. Augustin: Homilies on the Gospel of John, Homilies on the First Epistle of John, Soliloquies (ed. Schaff)