Where can I buy powdered Shrimp and Herring in the United States?

I have a recipe requiring these items and I live in a medium size, midwest town with only a Kroeger Supermarket. The ethnic foods isle does not have anything to offer along those lines. I would also like to purchase a product called Royco seasoning cubes. Is there a easy to navigate site that is dependable which would carry these items? Thanks for your help!