That's a standard Elixir roof vent cover available just about everywhere. Any Winnebago dealer will have them as well as most larger RV stores.
To help you, the part number you provided is for the complete Winnebago vent unit (cover, frame, cranks, screens, etc.) installed in your RV. The actual Winnebago part number for just the cover is 064470-01-700 Cover-Vent-non-powered. The actual Elixir model of that vent is V971201 which is what most non-Winnebago dealers and retailers will use to order a vent cover.
You also need to take into consideration that beyond just the cover, the entire frame and connecting rods and supports could have been damage. Replacing them part by part will cost you way more than what a brand new vent with installation will cost.
