There's a number of solutions to this problem, most of them I think would require some custom code. If you just wanted a straight list of emails from people that purchased a particular product, you could just make the following SQL query to your database:

SELECT DISTINCT(u.mail) FROM `uc_order_products` as p LEFT JOIN uc_orders as o ON p.order_id = o.order_id LEFT JOIN users as u ON o.uid = u.uid WHERE nid = {Node ID of particular product}