The "internal files" are found via the classpath when run on the desktop, so there is no simple way to "list" a directory in the classpath. If you're just using the desktop for development, and don't mind some hacks you can search "./bin/" for the missing files.
Like this:
**/ FileHandle dirHandle; if (Gdx.app.getType() == ApplicationType.Android) { dirHandle = Gdx.files.internal("some/directory"); } else { // ApplicationType.Desktop .. dirHandle = Gdx.files.internal("./bin/some/directory"); } for (FileHandle entry: dirHandle.list()) { // yadda ... }
For a bit more detail, see: http://bitiotic.com/blog/2012/05/15/libgdx-internal-files-hacks/