How to Fix Ductwork that I Crushed?
Looks like common 3 1/4" x 14" rectangular tin vent pipe, you should be able to buy it at any good plumbing shop. It sometimes comes with a locking seam along one edge but HVAC professionals often buy non-seamed pieces of various lengths. 

You may be able to beat that back into shape and use listed duct tape to patch it up. If not you will need to find the next upstream connection and replace the whole length.