You are correct. Tenabraex has cover ARD and not a threaded ARD. Leupold makes a number of sizes. The label might say Mark 4, but will fit. Only issue is that the sizes are limited: 30, 36, 40, 50 and 60 (probably for spotting scope).
Also, this might be something that Trevor at MK Machining might be interested in making 3-D printed. He has done similar, but he would need to see this as something that would sell in volume. The one-off cost, my guess, would be high.