It seems that I recall fender extensions being available as an option.
That said, my experience has been that I've most often wished I had fenders over the FRONT wheels on an open-cab tractor and primarily when I was running in "road gear" in the rain transporting implements. My present equipment is geared significantly lower, and probably capable of half the speed of the open cabs I used to run. I don't transport implements with my CUT. And if it's raining, I'm probably more inclined these days to drive a coffee cup than I am to run a tractor anyway.
Otherwise, under the conditions I use a CUT, I've never noticed mud being "thrown" - probably because I'm just not going fast enough to do it.