“Do you know of any “cast out angels” who believe Christ is their Lord and Saviour? I don’t.”
Let’s rephrase that.
Do you know of any “cast out angels” who believe Christ is their Lord?
Even the demons know Christ is Lord.
And they entered Capernaum. And on the Sabbath he went into the synagogue and immediately began to teach. [22]And the people were amazed at the teaching; for he was teaching them as one who had authority, and not in the way the scribes did. [23]And immediately in their synagogue there was a man in an unclean spirit, and he cried out, [24]saying, What do we have to do with you, Jesus the Nazarene? Have you come to destroy us? I know who you are—the holy one of God!” [25]And Jesus rebuked him, saying, “Shut up and come out of him.” [26]And the unclean spirit came out of him after convulsing him and uttering a loud cry. [27]And they were all awestruck, so that they asked one another saying, “What is this? a new teaching with authority! He even gives order to the unclean spirits, and they obey him.” [28] And immediately his fame spread everywhere, into all the regions of Galilee.
The demons certainly know Christ is Lord.
Just knowing and believing doesn’t mean salvation.
They certainly knew and feared the Lord.
However, again I'll ask you for evidence that any demon or fallen angel believes Christ to be their Saviour, which, of course, was the original question.