There are modern fan projects and ROM hacks that use the " Super Mario Land 4 " name to create a custom 8-bit adventure.
Since the third game in the series was Wario Land: Super Mario Land 3 , some fans consider Wario Land 4 for the Game Boy Advance to be the spiritual fourth entry. Download Super Mario Land 4
Below is an article exploring the mystery and the history of this "missing" sequel. There are modern fan projects and ROM hacks