Solved it. Here is how:
$myrows = $wpdb->get_results( "SELECT * FROM wp_postmeta WHERE meta_key = 'manufacturers' AND meta_value LIKE '%$manufacturer_id%'" );
foreach($myrows as $row){
$retailer_ids[] = $row->post_id;
}
Then run a WP_query with the post ids
$args = array(
'post_type' => 'where',
'post__in' => $retailer_ids
);
$retailers_query = new WP_Query($args);
The only reason I can see this having issues is if one of the serialized pointers is the same as a manufacturer ID. But there are ways to start them high so this workaround should be good for now.
