It's funny, but SPN got me listening to Kansas again (and got my kids interested in Kansas, too). A Kansas song that hasn't been used on the show that has a little of a western feel to it (while still being firmly a rock song of the era, late 70s) is Cheyenne Anthem. It's actually from the Native PoV rather than an outlaw or a cowboy. Parts of the long instrumental section make me think of the sound of trains, which were a part of the displacement of the Native Americans. And I always love the part at about 2:30 where the children's choir sings. Leftoverture is the same album that had "Carry On, Wayward Son" and you can hear a little of that in this song.