Any specialty lumber supplier in your area has a mill works they buy from. You will not be able to deal with the mill directly. I don't know who is in your town, but some one like 84 Lumber, or BMC West.
I have never had this type of request before, so I don't know what their willingness to process a small order would be. You may pay through the teeth.
Maybe using most as fire wood and making a mantle out of the best tree is a more feasible idea. You could cure it on your lot and have a local trim carpenter or cabinet maker trim it down and finish it to match your decor.