Different protocols, CHAdeMO talks CAN over dedicated pins, SAE CCS uses powerline encoding over some of the other pins. I would say almost guaranteed to not see a converter from one to the other because of the different protocols. By the time you have a processor in there and the heavy duty connectors it would be very expensive. All the DC fast chargers around here support both apart from ones at dealerships.
I'm guessing the software is just being lazy and asking the driver to specify which connector the car has to filter the charging stations on the map. Instead it should actually be able to read from the car which version it is equipped with (at least from the VIN, but also likely differences in the BMS software).
i just bought a 2017 so i hope chademo continues to be rolled out in new stations. hoping that new fast charging stations have both, especially since the new Leaf will almost surely have chademo, as it has up til now.