Ebay Germany, ok thanks John. I would not have figured that out.
I have not opened my Leo 1 kit yet, but I have seen some aftermarket instrucion sets for rotation units and I understand that there is nothing in there to make it rotate from tamiya.
Someone that has one would have to photo it and post the mating turret and ring here for you to see.
I am very interested in your project and want an early 1a1 turret. If I couldnt get one I would probably not open the kit I have as I didnt want the a4 turret.