Ok. I know WHERE horse manure comes from but I don't know WHERE I can get it and how I can transport it to my home.
Perhaps I should look on Craigslist?
See if there are any nearby riding stables or horse race tracks. Also, if there are feed stores, they might be able to tell you about any stables. You can also check Craigslist. You'll probably have to haul it yourself, in a truck bed or some kinds of containers like 32-gallon trash cans.
You may also be able to find composted manure at landscape companies, they deal in large quantities and will deliver.