Kent State University Press, or from the usual outlets such as Amazon. (Amazon usually has it for a lower price, and sometimes lists third-party suppliers with even lower prices.)
Although it's an academic journal, all issues of the Review so far have been very accessible, with informative articles that work for the general reader and fan, not just the Eng. Lit. scholar.
This new issue is made up almost entirely of fragments of Bradbury's own writing. As such, it will be a useful resource for the Bradbury scholar, as it gives direct access to so many story openings and undeveloped raw ideas. But this also will appeal to those who just love Bradbury's writing. It's like being allowed to look through Bradbury's personal files and getting a glimpse of work in progress.