Historical evidence for a separate Jewish branch of Christianity?

I've met some non-Hebrew people who have come from a Protestant background, become fed up with their faith, changed churches, etc and now call themselves Messianic Jews. This comes with some claims of things like - They are the true church. - Messianic Judaism developed in parallel with Christianity. - Messianic Judaism is somehow "more authentic" than the Christian church. What I'm interested to know is this: what type of historical evidence is there to support the claim that the church of the Holy Apostle James in Jerusalem was populated only by gentiles and the "Messianic Jews" maintained their own, separate congregation? Or that this happened anywhere else? I know Scripture records that the Apostle Peter started doing something like this to a small degree and was rebuked by St. Paul but that seems to support the opposite conclusion.