Я нашел ответ, просто используйте его на sidebar.php или в любом другом месте, где вы хотите, чтобы архив появлялся:
<?php
global $wpdb;
$limit = 0;
$year_prev = null;
$months = $wpdb->get_results("SELECT DISTINCT MONTH( post_date ) AS month , YEAR( post_date ) AS year, COUNT( id ) as post_count FROM $wpdb->posts WHERE post_status = 'publish' and post_date <= now( ) and post_type = 'post' GROUP BY month , year ORDER BY post_date DESC");
foreach($months as $month) :
$year_current = $month->year;
if ($year_current != $year_prev){
if ($year_prev != null){?>
<?php } ?>
<li class="archive-year"><?php echo $month->year; ?></li>
<?php } ?>
<li><a href="<?php bloginfo('url') ?>/<?php echo $month->year; ?>/<?php echo date("m", mktime(0, 0, 0, $month->month, 1, $month->year)) ?>"><span class="archive-month"><?php echo date_i18n("F", mktime(0, 0, 0, $month->month, 1, $month->year)) ?></span></a></li>
<?php $year_prev = $year_current;
if(++$limit >= 18) { break; }
endforeach; ?>
Стиль по своему вкусу.