Try Dead Link Removed. They are great and Tonia is very helpful. I've gotten Walnut this big from them and they will cut to size for you at very reasonable prices. They are in Toledo Ohio and they are reasonable on shipping. I've used them for wood for all three of my camera builds. Great family business.
If you're looking for relatively small amounts, you could try a local custom kitchen cabinet shop. They might even have "short ends" that will fit your needs.