Not all Zoethecus cones are the same thread size. I have 2 Zoethecus 4 shelf stands. When I moved, I found that the thread size was not the same on both racks. The cones were not interchangeable.
I have seen cones for sale on occasion on Ebay. But aftermarket is a good way to go. I don't think there is anything special about the cones. BTW at least one of my Zoethecus racks came with both cones and sliders.