I never asked where to buy Homosote to begin with and I certainly know how to use a website "Find a retailer" function. All responses to my questions have been very helpful and I thank all of you. I think "Homacote" is made by the same company that makes Homasote, thus the name similarity.
I'm leaning toward a foam layer over my 3/4 inch plywood base instead of Homasote.