Short answer: check major metasearch engines + the carriers that fly CMB–MAA, then book on the cheapest reliable channel (often the airline). The best places to find deals are:

1. Google Flights — excellent for fast price calendars, date exploration and price tracking. Use it to spot the cheapest days and set alerts. (Google.com)
2. Kayak — good for comparing many OTAs and shows booking-window guidance (their data suggests very short advance windows can be cheapest on this route). (Kayak.com)
3. Skyscanner / Momondo — useful for broad searches and month-view “cheapest month” comparisons for international/regional fares. (Skyscanner.net)
4. Regional OTAs (MakeMyTrip, Cleartrip, etc.) — sometimes show lower fares or local promos for Sri Lanka–India routes; check them after you find a target fare. (MakeMyTrip.com)
5. Airline websites — IndiGo, SriLankan Airlines and Air India run daily non‑stop services; once you find a good fare on a search engine, compare the airline’s own site (sometimes matches or beats OTA prices and gives better change/refund handling). (Google.com)

Quick step-by-step to get the best deal

• Search by month (Google Flights / Skyscanner) to find the cheapest travel window. (Google.com)
• Use flexible-date +/-3 days or “cheapest month” view. (Skyscanner.net)
• Set price alerts on Google Flights and Kayak. (Google.com)
• Compare the OTA price with the airline’s site before booking (book on the airline if prices are close — easier customer service). (MakeMyTrip.com)
• Watch baggage and change/cancellation terms — the lowest fares often exclude checked bags or have strict change fees. (Compare total price, not just base fare.)

Timing tips

• Search widely: some tools report November/June as cheaper months for CMB–MAA depending on year/market; low-season and mid-week departures tend to be cheaper. (Kayak.com)
• Kayak’s analysis shows short booking windows (around 1–2 weeks before) can produce very low fares on this short-haul route, but that can vary—use alerts. (Kayak.com)

If you want, tell me your exact travel dates or a date-range and whether you prefer nonstop, and I’ll scan current fares and give 3 cheapest options (with links and the airline vs OTA recommendation).