I don't think many places have it, which is too bad because it was Walt's favorite meal. At Disneyland, they serve "Walt's Chili" at Carnation Cafe. You can get chili at Casey's Corner though - it's the same as they put on the hot dogs or fries. It looks like you can get a small bowl of it on the menu under snacks.
For what it's worth, there is a Skyline Chili in the Flamingo Crossings area which is about 15-20 minutes off property depending on where on property you're coming from.