I purchased my vent in Myrtle Beach. However, I found the same vent for you on Tweetys. Go to Tweetys.com and type in 50045 in part number search. Item number is N22-0678 made by JR products. price 36.52 in Black and N22-0677 pn 50035 in white.
I have tested mine for 45 minutes at 400 degrees which is my highest oven setting. Vent did not melt. Also I can hold my hand up to the exhaust and it is blowing pretty warm air but does not feel anywhere near 400 degrees being exhausted.
Take a look at new Winnebago's they are venting their convections. The vent they are using is a little smaller so I'm not sure of their part number. I've been told Tiffin is venting their convections at the factory also.
You will also probably need to order an adapter from the manufacture of the oven to vent out rear. (I did anyway) You then will have to use alum vent tape to connect the two together.
I did a lot of looking at different vents before starting. This was by far the best design I could find as far as functional (flapper with latch) and looks (outside cover). There is many complaints with some other designs that the flapper door latches often break. Hope this information helps. Good Luck.