I don't have the knowledge of Greek to be able to tell whether Μαρκιανοί would be a reasonable formation based on "Marcion." I put the Greek in the relevant place for reference.
There are, therefore, and there were many, my friends, who, coming forward in the name of Jesus, taught both to speak and act impious and blasphemous things; and these are called by us after the name of the men from whom each doctrine and opinion had its origin. (For some in one way, others in another, teach to blaspheme the maker of all things, and Christ, who was foretold by him as coming, and the God of Abraham, and of Isaac, and of Jacob, with whom we have nothing in common, since we know them to be atheists, impious, unrighteous, and sinful, and confessors of Jesus in name only, instead of worshipers of him. Yet they style themselves Christians, just as certain among the Gentiles inscribe the name of God upon the works of their own hands, and partake in nefarious and impious rites.) Some are called Marcians (καί εἰσιν αὐτῶν οἱ μέν τινες καλούμενοι Μαρκιανοί), and some Valentinians, and some Basilidians, and some Saturnilians, and others by other names; each called after the originator of the individual opinion, just as each one of those who consider themselves philosophers, as I said before, thinks he must bear the name of the philosophy which he follows, from the name of the father of the particular doctrine.