I usually write about food when I found, ate, or cooked. But I actually have never seen nameko in the United States. They are popular common mushrooms in Japan, as well as shiitake, shimeji, and enoki mushrooms. According to wiki and other sources, they are called butterscotch mushrooms in the U.S.
They are usually sold in a vacuum pack. It is rather rare to see them sold like in the picture at the top. In either case, they are not processed. So that they need to be washed and cooked before eating.
One major characteristic of these mushrooms is their slimy and slippery texture. They are often used in miso soup, and as one of the toppings of soba noodles.
I wonder that they are not cultivated in the United States. I miss those mushrooms.