Array ( [1] => Array ( [city_id] => 1 [name] => Волгоград ) [4] => Array ( [city_id] => 4 [name] => Краснодар  ) )

Array ( [0] => Array ( [city_id] => 1 ) [1] => Array ( [city_id] => 4 ) )

<div class="sclad">
      Доступно на складе:<br>
    <div class="row">
      <div class="col-sm-6">
        <?php
          foreach($city_names as $city){
              echo $city['name']."<br>";
        }?>
      </div>
      <div class="col-sm-6">
        <?php foreach($city_list as $p_city) {
          foreach($city_names as $city){
            if($city['city_id'] == $p_city['city_id']){
              echo "<span class='green'>В наличии</span><br>";
            }
            else {
              echo "<span class='red'>Нет в наличии</span><br>";
            }
          }
        }?>
      </div>
    </div>
  </div>