Find it in Asian markets, or in the international section of your grocery store. But if you don't have it, don't sweat it. Substitute rice vinegar. You know I always talk about contrasts in food. The Chinese are the best at this, and that's what I'm doing with this salad.
Raw vegetables provide some crunch, as well as spicy, sweet flavors.
But I also cook some of the other vegetables, like the beans and shiitake mushrooms, for contrasts in texture and temperature. You've blanched and sauteed before. But there are a few things to go over. As the beans cook, they release acids. The more water, the more diluted the acids become.