Paperback

If you are in the UK: Amazon.co.uk.  (cheapest postage)

If you are outside the UK:  Amazon.com

 

Bookshops

It is very unlikely to be stocked by bookshops, though they would probably order it if you so wish.

 

Ebook

Kindle

If you are within the UK: Amazon.co.uk Kindle

If you are outside the UK: Amazon.com Kindle