-1st method-
search for <a> links present in the website's demo (that you want to mirror)
just hover the link and you will see the exact URL (that you need so you can
mirror it using Httrack or something else ...). inspect the element (<a> link)
and copy the URL.

-2nd method-
simply inspect the website's demo and search form the <frame> element and look
at it's attribute src="URL that you need !!".

let me know if this 2methods works perfectly.

Ps : it's my first contribution on Httrack.Sorry for "bad english".