The grain of walnut is kind of unique, and so the only other wood that I can think of that would be kind of similar in grain is alder. BUT you can stain white oak, birch, hickory and many other species this stain color. It is a warm brown and your contractor should be able to make up a sample on another wood species for you. Maple is about the only wood that I can think of that would not take this dark of a stain very well~ it is too hard and even with wetting to open up the grain, it would be blotchy.

Thank you so much! I appreciate your suggestions :)