Isn't the Kroma also the same diameter (body, tailcap threads) as the C series? Do disregard this if it isn't, but if it is, you could use one of the lanyard rings for the rest of the C series. It wouldn't use that gap in the tailcap, but instead would be a wire ring that fits between the body and the tailcap. It doesn't have the resistance to turning that the A2/etc. lanyard rings have, which can be quite nice, but it gets the job done.