I just got some of the new GT Cobra buckles from ITW Nexus in the mail — exciting times! These are plastic versions of AustiAlpin's Cobra buckle, which you're seeing more 'n' more in the bagmaking world.
If you're looking for a heavy-duty, smash-proof buckle, here ya go.
As of this posting, these aren't available yet for small-quantities buying, but I imagine they will be real soon. Keep checking Mil-Spec Monkey.