Just following up that I still haven't found a seat cover. To be truthful, I really haven't been looking that hard either. Still using the original plastic to try and keep it clean but not much life left in that.
My original plastic tore the first time I got back out and my pocket knife clip caught on it. Wife bought a large bath towel at Wally-World, and I threw that over it and tucked it in. Seems to be working fine.