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.
I also have OEM Gretsch 6" 4-hole hoops. They exist. I bought them to put on my Tama octobans because the original hoops were so flush with the bearing edges.
Thanks to all the above for letting me know about these DC hoops! I figured if they were out there, someone here would know. And, yes, I've no doubt that they are pricey!