(and, most immediately, supporting the petition for certiorari in McDonald v. City of Chicago, in which the Court could decide on incorporation): It’s available here, and it’s signed by Jack Balkin, Randy Barnett, Michael Kent Curtis, Michael Lawrence, and Adam Winkler.
Of these, only our own Randy Barnett is known as a general pro-gun-rights from the conservative or libertarian (in his case, of course libertarian) camp, though Lawrence might also be a left libertarian (I don’t know him as well as I know the others).
On the other hand, Balkin is a noted liberal. Curtis is also a liberal, though one with a lower public profile (but to my knowledge highly respected among law professors, and certainly highly respected by me, as a legal historian). Winkler is a liberal, a prominent critic of the Heller decision, and a supporter of the constitutionality of the D.C. handgun ban — he had filed a brief, together with Erwin Chemerinsky, on D.C.’s side in Heller.