Most basic sushi just starts with cucumber, maybe avocado, carrot, perhaps going a little beyond and doing a Japanese omelette topping, and obviously seaweed. I wouldn't consider fish to be part of any first attempt at sushi. It's all about the rice and vinegar and getting handy at working with it.
If you're in Seattle, you can also go to Uwajimaya, which will sell you every type of seafood you'd find at a typical sushi joint and the knife you'd use to prepare it. It's really not hard at all to make sushi at home!
I'm not sure if I'd trust those two sources. Whole Foods was known for having sushi-grade ahi, but a lot has changed since Amazon bought them. Most upscale grocery stores should be ok.
Sandworm101 seems to be thinking of sashimi.