I've used
www.7dayshop.com in the past. I think they trade from Jersey to get round the tax law, but have never had problems with postage from them.
Either that or check the usual sources like
www.ebuyer.co.uk,
www.microdirect.co.uk,
www.savastore.com,
www.aria.co.uk or even Amazon. Also, Tesco has a Jersey shop so they might do them cheap online too?