Sea vegetables can be found at most health food stores, Asian markets and in some regular supermarkets. You will most often find them in the “International” section with Asian foods like noodles and tofu. They come dried and pre-packaged. Most need to be soaked before consuming, although you can eat most of them as-is.
Dulse also comes in dried flakes which makes it easy to sprinkle. Kelp comes in powdered form which is convenient for adding to smoothies, but I prefer whole kelp to powder for overall freshness and potency of nutrients.
It is vitally important to choose organic sea vegetables whenever possible. The reason for this is that seaweeds have a great ability to absorb minerals from the water around them. Unfortunately, they also absorb all the bad stuff in the water around them too including heavy metals (mercury, arsenic) and other contaminants. Certified organic sea vegetables should be tested for heavy metals, fuel oil residues, PCBs, pesticides, herbicides and bacterial contaminants.