/includes/languages/english/mostlygrey/product_info.php

and the contents of product_info.php

are as follows:

<?php

define('TEXT_ONE_LEFT', 'Are you feeling lucky, only 1 available!');
define('TEXT_TWO_LEFT', 'Don\'t miss out, only 2 left.');
define('TEXT_THREE_LEFT', 'Hurry, while supplies last!');

?>