The journey from Gangtok to Raipur covers roughly 1300 km. You must first reach NJP or Bagdogra. From NJP, you can take a train to Raipur Junction. Flights from Bagdogra to Raipur usually connect through Kolkata or Hyderabad.
Total Distance: 1300 km by road, 1000 km air distance.
Ensure you book a train that stops at Raipur Junction.
Kolkata is the most convenient hub for this connection.
October to March for pleasant weather.