Its just as easy to make it yourself and also twice as fun!
I first made sushi nearly two years ago, after returning from China and inevitably exploring London's China town and the chinese supermarkets. I think the best thing about making sushi is picking the things you like best to go inside. If you really hate avocado, take it out. If you are in love with cucumber, stuff it in, its all your choice.
The same goes for the meat element, there is a huge variety of meat and fish you can choose from, such as beef, duck and chicken to salmon, tuna, crab, prawn and eel. You can even stick to a simple, good old vegetarian options, such as omelette, tofu or one of the best being philadelphia (or cream cheese to be correct).
Now, forget thinking you need a million and one things to make it.
The key elements to sushi are:
1) Sushi Rice (japanese rice)
2) Nori Sheets (Dry Seaweed)
3) Mirin - (rice wine vinegar)
4) Makisu - Bamboo rolling mat
5) Vegetables (eg cucumber, carrot, avocado)
6) Neta - raw fish/meat
Tip: My best advice is go to a chinese supermarket for these products. They are better quality and half the price of those in western supermarkets, plus its all part of the experience.