Searching the forms, I saw 3 ways to accomplish this...
1. Using sendmail and add an additional email address separated with a comma.
See posts #3 and #4 for details here:
http://forum.x-cart.com/showthread.php?t=1499
2. Create a new template file (such as a copy of the order completed template) and add it to the list of templates that are processed via the func_send_mail in include/func.php.
See post #3 for details here:
http://forum.x-cart.com/showthread.php?t=6273
3. See Post #22 in this thread...
Multiple email notifications:
http://forum.x-cart.com/showthread.php?t=19973
Also, there is a thread that deals with changing the "TO" email field in the func_send_mail file.
That is in post #4 here:
http://forum.x-cart.com/showthread.php?t=19008
One or some combination of those should do the trick for you.
Please share your final solution here once you get it working.
Good luck!
Robert