I have been speaking about the Jewish Christian Gospels outside of the New Testament, but you may be interested in the surviving quotations or allusions to them in the sources. If you go to Peter Kirby’s website http://www.earlychristianwritings.com/, you can read about the contents that have been assigned to the so-called Gospel of the Hebrews, Gospel of the Ebionites, and Gospel of the Nazoraeans. Of course, this is presuming the three Gospel hypothesis. Those who argue for a single Jewish Gospel would include all these traditions in the Gospel according to the Hebrews, since the latter two Gospels are hypothetical constructs of modern scholars. Those who argue for two Gospels would accept that all the traditions of Epiphanius go back to a distinct Gospel that modern scholars have dubbed the Gospel of the Ebionites, while they would reject the existence of the Gospel of the Nazoraeans and assign Jeromes’ fragments either to the Gospel according to the Hebrews, to Jewish Christian traditions that were contemporary with Jerome, or to an Aramaic translation of Matthew composed by the Christian Nazoraeans.
Reconstructions of the Gospels according to the Hebrews, Ebionites, and Nazoraeans Online