The first port of call for anything else should always be local shops and business, including sole traders and co-ops, as it keeps money in your local community for longer. See here (it’s about food, but it applies to everything else too).
If you can’t find local suppliers, the Co-op or John Lewis / Waitrose (an employee-owned company) might have it. Find your local Co-op store here, and your local Waitrose store here, or shop online.
Then there’s Fairmondo. It’s a new, co-operative alternative to eBay. It’s small at the moment, but you can help it grow, by joining, buying and offering products and services.