I'm not sure which would be best forum for this as this route spans two continents. There are no direct flights between the two countries but looking at flying in late March. Here are options
showing on Kayak.
!) Least expensive involves flying through India. One flight involves flying to Mumbai on Air Mauritius and then two hour layover to fly on to Sir Lanka. I presume I would have to go through immigration and pick up bags and then check in to Sri Lankan Airlines. I would have to get a visa on arrival (US Citizen)
2) Air Seychelles - I would fly from Mauritius to Seychelles - 6 hour layover in airport and then fly on to Colombo. Around $700 - also these flights are only a few times a week.
3) Emirates - fly from MRU to Dubai - 2 to 3 hour transfer in dubai and then on to Colombo. Most expensive route - $800 plus but looks like best airline/

Any recommendations?