OK, in: includes/templates/Drop6/templates

I have the following files:

tpl_subscribe_confirm_default.php (size: 2.04 kb)
tpl_subscribe_default.php (size: 2.17 kb)
tpl_subscribe_header.php (size: 1.30 kb)
tpl_unsubscribe_default.php (size: 1.85 kb)