I could not locate any replacement bushings for the large, lower control arm; it is only sold as a complete replacement part, and is quite expensive.

A mechanic friend of mine says that most manufacturers won't spec replacement ball joints or bushings for aluminum control arms because the act of removing and installing the bushing, assuming that is even possible as the bushing's steel sleeve may have galvanically welded itself to the aluminum control arm, damages the aluminum to the point that the interference fit cannot be assured. I think the E70 rear lower control arm is aluminum.
It sure would be nice to replace those 2 big inner bushings. Despite having replaced everything else back there, there's still a slight side to side looseness in the rear of my E70.