Elmore Leonard, who wrote the books that "Justified" is based on, also has a bunch of good Westerns, many of which became movies. A personal favorite, not quite a Western, is "The Hot Kid', which has a lot of gunplay and seems to me to be a precursor to the Raylan Givens stories.
"Mountain Man", by Vardis Fisher, became "Jeremiah Johnson"
"The Big Sky" series by A.B. Guthrie
"Welcome to Hard Times"
"The Last Hunt"
"Jeremiah Johnson" was based on a book entitled "Crow Killer." It was the real story of Liver-eating Johnson.
