I had a failure four years ago and had mine replaced in France by Renault. It was quite expensive.
The official procedure for replacing the box is indeed to take the whole drivetrain out. It isn't necessary, though. Also, the boxes can be renovated. When I had a failure, I found a place in Berlin, and I know others have had theirs done by the manufacturer. It does of course take the car off the road for a good while.
Anyway, good luck finding one