Where is the chadar from the Dhoti / Chadar set?
The standard dhoti length is approximately 4 meters. For the dhoti/chadar sets, the chadar can be attached to the dhoti on the same strip of cloth, so the cloth could be longer than the standard 4 meters. You can cut the extra cloth to make 2 pieces: one piece for the dhoti and one for the chadar.
There would be a place about 1/3 of the way from one end or so where it can be cut to be separated. The place could be indicated by a line of loosely woven fabric that might even look frayed. The cloth can be cut on either side of this line.