Add custom metabox with all available shortcodes

function add_shortcodes_metaboxes() {

    add_meta_box('available_shortcodes', 'Available Shortcodes', 'available_shortcodes', 'page', 'side', 'default')

}

add_action( 'add_meta_boxes', 'add_shortcodes_metaboxes' );

function available_shortcodes() {

    global $shortcode_tags;

    foreach ($shortcode_tags as $shortcode_tag => $description) {

        echo $shortcode_tag.'';

    };
}