I'm not aware of Gretsch die cast hoops in this size. Even new USA custom drums show only an 8" as the smallest size. Are you looking for modern or vintage? When Gretsch made their own DC hoops, they offered nothing smaller than the 12" 5-lug hoop. All smaller diameter toms had triple-flanged hoops. Maybe others know something I don't and will chime in!
They do exist (I have a bunch but they are all being used). When Gretsch first brought out their smaller concert style toms they used off the shelf triple flange hoops for them but at some point they did spend the money on casting dies for hoops in those sizes. They no longer seem to offer a 6" tom though and therefore neither do they make the hoops.