Call your dealer first. I seem to recall that only certain colors are still available. Now, the dealer price is going to be very high; last I looked, it was several hundred dollars per panel.
You'll probably wind up looking for complete used seats. Hard to find in top shape, but cheaper and easier. Aftermarket covers do exist, but the ones I've seen are not a perfect match, and you'll have the tricky task of transferring the heating elements.