Mike,
The Stoysich in West Omaha at 132nd and center has small bags of chunks (perfect for the WSM) located right under the meat counter. Las week I saw pecan, mesquite, and cherry, and in the past I've seen hickory and apple. In general, the Stoysich folks are very helpful, so if they don't have what you want, they can probably get it for you.
Uncle Earnie's is formally known as Uncle Earnie's Riverside Inn, located in Plattsmouth about 30 minutes south of Omaha on highway 75. Head south on 75, past Bellvue. You'll see his place just on the other side of the river. Uncle Earnie has been winning cookoffs right and left in the area. His restaurant is a bit divey, which some folks prefer in a Q joint. He had big bags of chunk wood for sale, too, although I didin't notice what kind.
In fact, if you keep driving south on 75 there are some orchards between Plattmouth and Nebraska City. You could stop in and ask if they sell firewood. That's what I do out here in California. There are lots orchards aroudn here. I stop in to buy fruit and ask nicely if they have any fruit wood. Usually they do, and often they'll just give it to you for free.
Whether you hit up Stoysich or Uncle Ernie, either way you'll come home with wood chunks, and some good meat. Not a bad trip for a BBQ fan!
Take care,
Henry Joe