The expected location of
importbuddy.php is inside the actual backup at
/wp-content/uploads/backupbuddy_temp/xxxxxx/ where the
xxxxxx will be a folder with the serial code name that matches the one in the name of the backup. You will need to extract the backup archive in order to obtain this importbuddy.php file.
Since importbuddy.php files aren't connected to any specific site or backup file, you can use an importbuddy.php file from any site (as long as you know the password connected to that other site's importbuddy). You can find other ways to recover the importbuddy file, and set a new password in this article.