$query = array(
    'post_type' => 'product',
    'posts_per_page' => -1,
    'meta_query' => array(
        array(
            'key' => '_stock_status',
            'value' => 'instock'
        ),
        array(
            'key' => '_backorders',
            'value' => 'no'
        ),
    )
);
$wp_query = & new WP_Query($query);
while ($wp_query->have_posts()) : $wp_query->the_post();