Supermarket have kits and books. At least Sainsbury's and Tesco do.
Well, by kit I mean they sell constiuent parts.
You only need:
Bamboo Mat
And
Short-grain Rice
Nori
Rice Vinegar
Sushi Vinegar
And
Pickled Ginger
Spicy Wasabi Horseradish
Dark Soy Sauce
And
Obviously fish etc.