The D.C. government's petition for certiorari in the D.C. gun ban case is here, via SCOTUSblog. It's a somewhat unusual petition: it spends relatively little time on the split and its consequences, and instead uses much of its space to argue the merits (usually pretty irrelevant at the cert stage). I gather the authors figured that a grant was pretty much a given; in light of that, no harm in taking the opportunity to start arguing the merits.