I have never done the Indian Ocean ports, but have done many other ports around the globe, & one things for sure there is never ever a shortage of private hire/taxi's waiting to relieve you of the contents of your wallet to go on a tour when a cruise ship arrives. Have you 'googled' the ports in question? Have you looked at other cruise forum websites? The info is out there......
Yes, you will find various tour companies on the net who are raedy and eager to do this for you. The alternative is to look at the ports tourist site together with the ship's tours and from that pick what you would like to see or do then work out you own itinerary and armed with that schedule negotiate with the taxi drivers who will be on the quayside and get yourself a deal. As I have said on many previous occasion if you do your homework you'll get good results. ... Neil.
Look in the PORTS section of this site - very useful.