Welcome to the forum!
Out of curosity, is the vent broken or just very discolored. The vent and be masked off and painted with a quality paint for plastic. If it needs to be replaced, you could try contacting the parts/warranty department for Cardinal...unfortunately I don't have a phone number for you.
Nights camped in 2011 - 43, 2012 - 45, 2013 - 55