Any student edition of Plato’s Republic following the format of Pharr’s Aeneid 1-6?

And in general, did Pharr’s approach catch on for the preparation of student editions of other texts?

Book One, yes: several, which I’ve listed elsewhere.

Book 10: Cambridge Green & Yellow.

Otherwise, not any that I have been able to find.

Yes, in the sense that there are other texts that have a similar format. One author in particular, Geoffrey Steadman, produces many such texts. But other authors also create “Steadmans,” as they are sometimes called.