A paperback edition of Unknown Quantity was brought out in May 2007 by Plume, a division of Penguin Books, U.S.A. (New York).
A U.K. hardback edition of Unknown Quantity came out in April 2007 from Atlantic Books of London. Atlantic also published the U.K. paperback edition in April 2008.
There have been various translations, not all of which I possess. Shown below are the editions and translations I do possess.
I have a dozen or so copies of each translation, so if you'd like one, please email me at the e-address on my home page.