We’re all constantly re-loading THIS AMAZON PAGE:
…that lists the Legend Of Korra, Book One: AIR Blu-Ray. It used to have a pre-order option, but it got downgraded to a sign up alert.
BUT – it hasn’t been pulled down, so we’re holding out hope. If it’s hitting around lat May like we hear the DVD is, expect this page to transform into a pre-order page soon. I’m not sure why they’d withhold the Blu-Ray, but at least Amazon has the HD episodes available on Amazon Instant.