The short answer is that which was said above: get SmartDashboard running (which I think you can select in the DS if you set it to "Java Dashboard") and the autonomous chooser will just show up. However, customizing SmartDashboard and (in particular) making it pretty is fairly annoying.
With that in mind, I'll give you another option: pynetworktables2js
It makes building a dashboard and interacting with the robot as easy as making a webpage! The example program has an 'autonomous.html' page that shows a combo box which lets you choose autonomous modes.
https://github.com/robotpy/pynetwork...master/example