However I do not see anything for the C128 nor for the C128D keyboard. Were there any made?
I have a dark brown, vinyl cover for the flat C128. And somewhere in the house, I have the more-preferred, fabric cover for the flat C128. Why preferred? Because you could cover a just shut-down C128, and the C128's internal heat would still dissipate through the thin fabric.
I have both a plastic one (with a clip-on hinge to open without completely removing it) and a fabric one. You can buy the fabric one from Vesalia, the plastic one sometimes appear on eBay (there's one on auction right now, look for this item #: 151875856851)