Are there any natural cures for mania?

No: I am not aware of any cures for mania - natural or via treatment. Continued treatment can control symptoms but relapses might still occur.

Well, yes: The oldest and best known treatment to prevent mania--lithium--is a naturally-occurring mineral salt whose therapeutic benefits were first applied to kidney stones. Slowly, their beneficial effects on mania were discovered. Like digitalis--an extract of foxglove found to be helpful for "dropsy", then created in pure form as digoxin--many modern psych medications are natural, just purified.