Grave of the Fireflies is out-of-print in North America. If that isn't a shocking indictment of the state of the anime business on our shores, then nothing is.
Unfortunately, since Disney now holds the distribution rights to the Ghibli films, and future DVD or Blu-Ray release would have to go through them. In a perfect world, Disney would give Fireflies and Omohide Poro Poro to The Criterion Collection. But that's about as likely as....(fill in the blank).
Shocking, really. This is just about the greatest animation movie ever made, and there's next to no chance of it ever being seen in the US again.