Greetings Harley:
You would be surprised how many woodworkers here in the Midwest who want both air-dried and kiln-dried lumber for their wood working projects.
Some of our state's American Tree Farmers--those of whom own and operate a small sawmill--typically utilize the Internet; market their lumber to local forestry groups such Tree Farmers, state landowner/forestry association members, Farm Bureau members, and local woodworker clubs/stores; and they utilize their state forestry agency staff to help them market their lumber to a wide and diverse audience of prospective buyers.
I know many tree farmers who have sold lumber using Ebay, www.woodweb.com, and www.woodfinder.com
If this doesn't work for you, please contact your local state forestry agency for additional assistance regarding market outlets for your black walnut lumber.
Best of luck!