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