If you haven't tried Bill at Radial Tire 301-585-2740 or 703-554-4803, I've read here on the forum quite a few times that he has them, although haven't heard lately.
Bridgestone produces the rear tires in batches. When one batch sells out, then they produce more. In the past there have been times when the rears weren't available for a few weeks or months. But call Bill at Radial tire to find out.