It is available as an ePub from Books on Board and also in the UK (e.g. from
WHSmith).
I use
ebookprice.info for any generic US-ebook searches now. It does not distinguish between Adobe ePub and PDF, but currently only Books on Board stocks ePubs.
EDIT: BoB says this is an ePub but it is also sold as "Adobe Digital Editions" by Powell's and Diesel. I tend to believe BoB on this (since there is a UK ePub), so other book stores may be selling ePubs - they just are not saying so.