Hi,
The product_code is not loaded by the MySQL query as it's not needed normally.
You also need to change the line:
$select = ' a.product_id AS id, a.product_name, a.product_alias, a.product_canonical, a.product_created AS created , a.product_description, "'.$new_page.'" AS browsernav';
to:
$select = ' a.product_id AS id, a.product_name, a.product_alias, a.product_canonical, a.product_created AS created , a.product_description, "'.$new_page.'" AS browsernav', a.product_code;
in that same file to get the product_code loaded.