How to add admin bar only page?

You have to create a new array for the new item and pass the parent parameter as the id of this already created item.
In your case, the args array should be like this:

$args = array(
    'id' => 'my-item',
    'title' => 'My Item',
    'href' => '#',
    'parent' => 'theme_page',
    'meta' => array(
        'title' => __('Click Me'),
    ),
);

This post has a complete explanation of how and where you can add items to the admin bar and the usage of the parent parameter.