mike, mirror or leather goldfish do not exist. the closest you could come to a mirror scale would be a hybrid fish, a mirror koi crossing with a goldfish.
it might be possible through selective breeding of metallic goldfish to matt/nacreous goldfish to create a nacreous fish with metallic scales down the dorsal fin as in mirror carp. however, that would take generations upon generations to create - and i'm not even sure if it is possible to secure the location of the metallic scales no matter how long you worked on that trait.
as for leather goldfish, the genetics just do not exist to create a fish without scales. however, a fully matt fish has transparent scales, allowing the underlying skin to show through. this is the closest one can get to a "leather" goldfish. these are commonly seen in the pet trade now and are popular among some breeders.