I got this nice list of articles on the Jewish concept of a priestly Messiah from Bill Hamblin’s blog:

Mason, E. You Are a Priest Forever: Second Temple Jewish Messianism and the Priestly Christology of the Epistle to the Hebrews (2008)

Higgins, A . I. B. “The Priestly Messiah.” New Testament Studies 13 (1966-67): 211-39.

Kuhn, Karl Georg. “The Two Messiahs of Aaron and Israel.” New Testament Studies I(1954/55): 168-80.

Liver, J. “The Doctrine of the Two Messiahs in Sectarian Literature in the Time of the Second Commonwealth.” Harvard Theological Review 52 (1959): 149-85.

Rainbow, Paul. “Melchizedek as a Messiah at Qumran.” Bulletin of Biblical Research7 (1997): 179-94.

Looks like some articles (well, the first one is a book) definitely worth looking at, if you can find them.