Fireball Forward and its scenario books can be ordered in the USA from the following distributors:
In the UK you can either:
Contact Lon at Brigade Games (see above link) and he will get you a copy at a rate that will help deflect the shipping cost.
Contact Cavalier Books and ask them. http://www.caliverbooks.com/
Contact North Star Figures and ask them: http://www.northstarfigures.com/ (should be available starting in September 2012)