Mumbai city sightseeing tour?

Surprisingly, i tried a lot in the internet to find some package tour operators in the city of Mumbai for local sightseeing tours. I am told there are some good travel operators available locally in Mumbai , who conduct package tours by Air conditioned buses to see Mumbai. I shall be very thankful if any one give me some info about this.since the car wallas charge exhorbitant monies, i wish to to take a A/C bus tour. please be informed.