Another in Raleigh.....
http://www.hoodindustries.com/distri...tions/raleigh/
Again, they don't list Butternut, but do carry large Basswood pieces. It's very likely that they would have Butternut.
There's a Wholesale store in Charlotte that has a large selection of wood and will sometimes have Butternut. I can't remember the name of the store, but IF you are near Charlotte, you can look it up in the phone book.
There are Woodworking supply businesses located in North Carolina that would (could) also carry Butternut or offer assistance in how to get it.
Woodcraft has stores in Raleigh and Charlotte. Woodworkers supply has one near Burlington. Klingspor (Woodworkers Store) has them in Hickory, Winston-Salem, Charlotte and Raleigh.