Hi,
I believe you are an old Virtuemart user. Because the path you gave was for VM1.1.xx, it is no valid for VM2.0.xx anymore.
Virtuemart uses these PHP files for emails:
/components/com_virtuemart/views/invoice/tmpl/mail_html_pricelist.php
/components/com_virtuemart/views/invoice/tmpl/mail_html_footer.php
/components/com_virtuemart/views/invoice/tmpl/mail_html_header.php
DarkMArt doesn't use template override for the confirmation email layouts. The original Layouts of Virtuemart for Confirmation emails will be the same with or without DarkMart. So, you need to modify these PHP files to make some changes on the confirmation emails.
You can use the "template overriding" for your modification on email PHP files, so you wouldn't need to make some changes on Virtuemart Core files. (which is an ideal way of usage). For more information about template overriding, read this article:
docs.joomla.org/How_to_override_the_output_from_the_Joomla!_core
Regards.