What if you use ORDER BY pm.meta_value ASC
in WP db class:
$r = $wpdb->get_col( $wpdb->prepare( "
SELECT pm.meta_value FROM {$wpdb->postmeta} pm
LEFT JOIN {$wpdb->posts} p ON p.ID = pm.post_id
WHERE pm.meta_key = '%s'
AND p.post_status="%s"
AND p.post_type="%s"
ORDER BY pm.meta_value ASC
", $key, $status, $type ) );
That will provide you an ASCending ordered array.