<?php
$args = array(
    'post_type'      => 'product',
    'stock'          => 1,
    'posts_per_page' => 4,
    'orderby'        => 'date',
    'order'          => 'DESC',
);
$loop = new WP_Query( $args );
while ( $loop->have_posts() ) :
    $loop->the_post();
    global $product;
    ?>
    <div class="span3">
        <li>
            <!-- HTML anchor and other stuff goes here -->
        </li>
    </div>
<?php
endwhile;
wp_reset_query();