以下是解决问题的代码：

$woo_args = array(
    \'status\'        => \'publish\',
    \'limit\'         => 1,
    \'stock_status\'  => \'instock\',
    \'brand\'         => 99
);
$products = wc_get_products($woo_args);

if (count($products) == 0){
   //No product with the custom attribute id=99
}

add_filter(\'woocommerce_product_data_store_cpt_get_products_query\', \'my_handle_custom_query_var\', 10, 2);
function my_handle_custom_query_var($query, $query_vars) {
    if (!empty($query_vars[\'brand\'])){
        $query[\'tax_query\'][] = array(
            \'taxonomy\' => \'pa_brand\',
            \'field\'    => \'id\',
            \'terms\'    => $query_vars[\'brand\'],
            \'operator\' => \'IN\',
        );
    }
    return $query;
}