Garden centres will have packed theirs away by now, ready to pull out again in August – just in time for next Christmas 😉
The cheap lights (well even the more expensive ones TBH) all come in from China (or similar) in containers in July / August. In general they aren’t held in the uk, I work for a chain of 30 garden centres and we have placed our orders now for next Christmas. Our supplier/importer will only import to match his orders, he will turn his hand to furniture or something else for the rest of the year. We sell what we can and then pack everything away in very deep, dark store cupboards until the following year. Suspect B&Q will be similar.
Tescos own Dobbies Garden Centres, so they will also work along similar lines.
Will candles in jam jars work… 🙄