Hi there. Are you talking about the Harbor Breeze Centreville ceiling fan?
Assuming that you are, it looks like this is a special order part and you may need to contact Harbor Breeze to find a cover to fit where the light kit was removed. If you have a 3D printer, you can also try making a cover that will fit in place – all you really need is something that suits the dimensions. However, we aren’t able to source this part. We looked but are unable to find one that specifically meets the dimensions you need for the Centreville fan