You don't need the vent with an electric model so you can remove and cover. Here is a source for every thing you would need.
https://www.airpartsinc.com/default.asp
Now the question is would it be easier to repair the cracked cover and leave the vent or buy the aluminum, buy the rivet and necessary tooling to buck rivet a patch in place. Oh is your interior panel out so you can access the buck rivet form the inside other wise you will want to use Olympic rivets which will need a rivet shaver $350.