Both destinations are served by Colombo (CMB). Since there's no flight route between them, the best way to travel is by road.
Erumeli
Fly to Colombo (CMB), then travel by road to Erumeli. Taxis, buses, and private cabs are available from the airport.
Madurai
Fly to Colombo (CMB), then travel by road to Madurai. Local transport options include taxis, auto-rickshaws, and state buses.