You can make this salad with virtually any kind of seaweed you find in clean waters on any North American shoreline. If you are not in North America, you will need to identify specific seaweeds to your oceans. In the Pacific, avoid the feather boa kelp, Egregia menziesii -- it's just too tough to eat in a salad. You will want to keep your seaweeds cool and moist for the drive home, then wash them in cool running water when you are ready to use them. Blanch if you want. Or eat the little crustaceans that hang onto the seaweed (protein!), whichever.
You can also buy seaweed. Look for wakame, which is the typical seaweed used in salads. You can find it in many Asian stores. It usually comes dried, and will reconstitute almost like fresh. Virtually every sushi restaurant in America uses the dried stuff, so don't worry.