I have come acroos a source for air dried butternut. This guy has a mill a few hours north of me and said the butternut has been air dried 5 years. I will be taking a trip up in the next few weeks so if anybody is interested in some butternut let me know and spread the word.
He also has other species including Arbor Vitae "White Cedar", black walnut, Italian walnut, Sycamore, cherry, Red Elm, Hard Maple, Black Locust, Honey Locast, Sasafrass, Poplar ect. ect.