These are places I have bought books:
I love this store. That’s all I have to say.
This is TTMIK’s store. They have a lot of books, audiobooks, book marks etc. Really, it’s Korean products galore. You can pay via paypal and your package will arrive in the mail.
SOAS Bookshop, Brunei Gallery Building, School of Oriental and African Studies, Thornhaugh Street, Russel Square, London, WC1H 0XG
Here you can buy the teaching materials that are used for the courses at SOAS.
Foyles, 107 Charing Cross Road, London, WC2H 0DT
Here you can buy both Korean teaching materials and regular literature. The Korean section isn’t huge, but there is enough to tempt you, and it is possible to order home books as well.
A Korean learner I met in the store advised that the search function on the website works best if you have the ISBN number for the book you want. The website is therefore better suited for buying something specific than it is for browsing for inspiration.
If you know of other places to buy material, do share!