- array_search: documentation ( source)
- var_export: documentation ( source)
<?php
$vacancies = 13;
$list_order_id = [1, 5, 6, 9, 10];
$last_id = 6;
$count = count($list_order_id);
$index = array_search($last_id, $list_order_id);
$result = [];
for ($i = 0; $i < $vacancies; ++$i) {
$result[] = $list_order_id[++$index % $count];
}
var_export($result);