As far as I know there are no laws on the federal level that require states to import assault weapons. So a state should be able to control what enters its own borders from another state, as long as it doesn't contradict any federal laws (which don't exist in this case). International imports may be another story.
But then, I'm no big city lawyer.
"And I'm tellin' you son, well it ain't no fun, staring straight down a .44"