I really love this soup. I am fortunate enough to live in NYC and have access to almost anything in terms of ingredients, and food. So for me finding Dashi stock (or actually the ingredients to make it) was not a problem. If you cannot find Dashi stock or the ingredients, I assume one could substitute fish or even vegetable stock, although I am not sure what the difference would be. I have included at the bottom of the soup recipe a simple Dashi stock recipe.