You'll rarely get anything better than grade 2 materials for the local one-way passenger missions.
The higher grades seem restricted to tourist trips.
This is false.
Take on allied status first class bulk passenger missions to systems at which the destination is 60k or more ls away from the main sequence star.
You will get payed 9 million credits and 4 to 5 G5 materials - or 10 to 12 mil credits - for around 30 1st class passengers, like tourists or businessmen.