In the world food isle in tescos there's a few different ones.
I like this one over the rest
http://www.tesco.com/groceries/Product/Details/?id=263413322
But really need to find a specialist one which has much more of a kick.
very easy to make and tasty
I've only made it once and I just googled one, just had a look to see if I can remember which one I did and I'm afraid I can't, but they are all pretty simple. Vinegar or rice wine, chilli, garlic, water, sugar type variations