Greetings Jolynn:
Here are my suggestions and in no particular order:
1) Contact your local state forestry agency office (Texas Forest Service) or the Texas Forestry Association to see if they have a newsletter where you can place an advertisement for this black walnut tree or if they know of local woodworkers in your area who may be looking for quality black walnut logs.
2) Contact your state Tree Farm committee and see if you can place an advertisement in their newsletter
3) Similar to items 1 & 2, place an advertisement in your local newspaper, woodworker shop(s), and Web sites such as www.woodweb.com and www.woodfinder.com
This will take a little work on your end, but I promise it will be worth the effort!