This link is broken, either the page no longer exists or there is some other issue like a typo.
This is link for SS 316 flex pipe at cost of $26/ft , cut to desired length. They will ovalize a section of the pipe so that it can pass thru the damper frame or rectangular damper opening and extend up as far as you want to clear damper. Must call to order 800-472-6728. Price seemed reasonable and they ship UPS for small lenghts so it kepps shipping cost low.