To borrow:
Social Media and Everyday Politics is available to borrow from more than 300 libraries in 28 countries around the world; many are listed in Worldcat, and if your library does not have the print or ebook versions, you can always ask your library to order it (including directly from the publisher; see below)!
To buy:
You can order the book from many of the usual online suppliers, but also through your local bookstore (highly recommended!). It’s available as paperback, hardback, and ebook, at reasonable prices (especially for the paperback). You can request a examination/institutional copy from Polity / Wiley.
If you prefer to go via Amazon/Book Depository/etc, you can find the book listings at, among others: