Wow I never knew they made a fastback hard top for the Miata! That looks sweet! Reminds me of the Spoon hard top S2K.
Custom stuff. There is a guy on the west coast that builds them from scratch. Mazda made one prototype of the NA (I have a pic on Flickr of it but can't access it), and there are a couple people in JDM-land who make them. Not factory pieces, unfortunately.