I think making your own is a possibility if you cannot find an acceptable commercial solution. I have not done it myself but am aware of two ways. Both need a backplate, maybe plywood.
- make a plug and form some plastic over it.
- make a foam spinner (the most low tech way is to fix a rougly shaped piece of foam to your motor and use that as a lathe). Shaping the inside of the cone is probably the most difficult part. Then you glue the finished spinner to the back plate and hope not to break a prop.