Local shops and business, including sole traders and co-ops: see here (it’s about food, but it applies to everything else too). Localbookshops.co.uk has a searchable listing of independent bookshops in the UK.
Alibris, although not a co-op itself, is a platform for independent bookshops, providing millions of books, many of them second-hand for less than £1.
Here’s the Fairmondo ‘books, ebooks, magazines, games & DVDs’ section. If you’re an independent producer, join Fairmondo here.