Releases of JOpt Simple are synced to the central Maven repository. Declare a dependency element in your POM like so:
... <dependencies> ... <dependency> <groupId>net.sf.jopt-simple</groupId> <artifactId>jopt-simple</artifactId> <version>6.0-alpha-3</version> </dependency> ... </dependencies> ...
If you're not using Maven, you can still download the newer releases from the Maven repository manually, here.
You can find older releases at SourceForge.