Chinkiang Vinegar: tangy delicious Chinese black vinegar is available at Asian markets and via Amazon. I highly recommend its use in this recipe for its incomparable flavor. This vinegar does contain gluten however so if this is an issue my best backup suggestion would be white rice vinegar.
The Mushrooms: wood ear mushrooms are the traditional choice in Chinese hot & sour soup - if you have access to them, by all means experiment. I don't think you will be disappointed with shiitake however, they have that wonderful chewy resilient texture and umami flavor that is positively delightful in this recipe.
The Broth: if you have a homemade broth (whatever version you enjoy) it would be an ideal time to use it in this recipe. Otherwise, a broth you typically use is fine.