WordPress Custom Post Type Archive

I have problem showing custom post type archive page. I want to share the code to create a custom widget which you can input the post type name and it will show you the archive (year and month) for that custom post type. You can edit it as needed.

<?php
class custom_archive extends WP_Widget {
function custom_archive() {
parent::WP_Widget(false, 'Custom Archive');
}
function form($instance) {
// outputs the options form on admin
$post_type = $instance['post_type'];
$title = $instance['title'];
?>
<p>Title:<br /> <input name="<?php echo $this->get_field_name( 'title' ); ?>" type="text" value="<?php echo esc_attr( $title ); ?>" /></p>
<p>Post Type:<br /> <input name="<?php echo $this->get_field_name( 'post_type' ); ?>" type="text" value="<?php echo esc_attr( $post_type ); ?>" /></p>
<?php
}
function update($new_instance, $old_instance) {
// processes widget options to be saved
$instance = $old_instance;
$instance['post_type'] = strip_tags( $new_instance['post_type'] );
$instance['title'] = strip_tags( $new_instance['title'] );
return $instance;
}
function widget($args, $instance) {
// outputs the content of the widget
extract( $args, EXTR_SKIP );
$post_type = $instance['post_type'];
$title = $instance['title'];
?>
<?php echo $before_widget; ?>
<?php echo $before_title . $title . $after_title; ?>
<ul>
<?php
global $wpdb;
/**/
$years = $wpdb->get_col("SELECT DISTINCT YEAR(post_date) FROM $wpdb->posts WHERE post_status = 'publish' AND post_type = '".$post_type."' ORDER BY post_date DESC");
foreach($years as $year) :
$years_count = $wpdb->get_var( $wpdb->prepare( "SELECT COUNT(*) FROM $wpdb->posts WHERE post_status = 'publish' AND post_type = '".$post_type."' AND YEAR(post_date) = ".$year.";" ) );
?>
<li class="year"><a href="<?php echo get_year_link($year)."?post_type=".$post_type; ?>"><?php echo $year; ?></a> (<?php echo $years_count; ?> Posts)
<ul>
<? $months = $wpdb->get_col("SELECT DISTINCT MONTH(post_date) FROM $wpdb->posts WHERE post_status = 'publish' AND post_type = '".$post_type."' AND YEAR(post_date) = '".$year."' ORDER BY post_date DESC");
foreach($months as $month) :
$months_count = $wpdb->get_var( $wpdb->prepare( "SELECT COUNT(*) FROM $wpdb->posts WHERE post_status = 'publish' AND post_type = '".$post_type."' AND YEAR(post_date) = ".$year." and MONTH(post_date) = ".$month.";" ) );
?>
<li class="month">>
<a href="<?php echo get_month_link($year, $month)."?post_type=".$post_type; ?>"><?php echo date( 'F', mktime(0, 0, 0, $month) );?></a> (<?php echo $months_count; ?> Posts)
</li>
<?php endforeach;?>
</ul>
</li>
<?php endforeach; ?>
</ul>
<?php echo $after_widget; ?>
<?php
}
}
register_widget('custom_archive');
?>