where do I buy these books?

Ты can order them from амазонка или from BBC Магазин - just Поиск for BBC Merlin on their websites. If Ты live in the UK, I think Ты can also buy them in some of the bookshops like Waterstones, at least, 2 years назад I saw them in London.

...You sure those aren't DVD cases? Umm there are several Книги on "goodreads. com " but they are pretty much Цитаты on the shows...dunno...

SIMPLE Ты CAN BUY THEM IN BOOKSTORES LIKE NATIONAL BOOKSTORES.