Only showing products that are in stock

I have a page that I produced for a client some time ago, which shows plants and flowers in various categories: e.g. http://www.colourparadise.com/plantsSubcategory.php?main_category=13. I've added a new drop down menu - called "availability" - in CMSB so they can choose if a product is "In Stock Now" or "Unavailable". Is it possible to show in the bullet list only the plants where "In Stock Now" has been selected?

This is the code that displays the bullet list:

    <ul><?php foreach ($product_detailsRecords as $detailRecord): ?>
     <li>
       <a href="<?php echo $detailRecord['_link'] ?>"><?php echo $detailRecord['title'] ?></a>
             <?php endforeach ?>
          
              <?php if (!$product_detailsRecords): ?>
       </li>
    <?php endif ?></ul>