I was addressing the last part of your statement and should have clarified that. You wrote...or their Christian ancestors were never a part of the Roman Church.
Unless you are speaking of the Orthodox church after the Schism of 1054(?) your statement is not historically accurate.
No Protestant denomination which holds with orthodox Christian teaching such as the Divinity of Jesus, The Holy Trinity, that Christ is both fully God and fully man would want to claim some kind of relation with people who broke away from the early Church. They were by both their contemporary Church and modern Protestant definition heretics. They were Gnostics, Arians, Nestorians. They were not some hidden remnant that reemerged when the hammer pounded on that Wittenburg(sp)door.
If they have any descendants it is the Jehovah Witnesses, the Oneness Pentecostals, the Unitarians, the LDS and other sects which deny orthodox teachings about Jesus.
You're correct no Protestant denomination because those Christian Churches broke away during the Reformation and thus have been labeled Protestant (protesting what they broke away from). However, there have always been Christian Churches that were not a part of the RCC, or EO.
Even during Jesus' ministry on Earth we see in Scripture churches that were not under the authority of the Apostles, but were acceptable to Jesus.
Luke 9:49-50 Now, John answered and said, "Master, we saw someone casting out demons in Your name, and we forbade him because he does not follow with us."
But Jesus said to him,"Do not forbid him, for he who is not against us is on our side."
The Didache, which was only discovered around 150 years ago reveals the local autonomy of early Christian Churches. Prior to the Reformation the Donatist's left. The Montanists, Novatians, Paulicians, Albigenses, Paterines, Petrobrussians, Henricians, Waldenses and Anabaptists all existed prior to the Reformation. Our understanding of these various Christian Churches is limited because during this period the RCC had emerged as the dominant State sponsored church. It was never in the RCC best interest to keep accurate records of these various Christian Churches and if they became large enough they were treated as a threat to the State.
Emerging from the Anabaptists you have Baptists, Quakers and Mennonite churches today.