The closest airport to Bac Ha is the Dien Bien Phu Airport, and no direct flights are available from India to Vietnam. Airlines that provide these services include Vietnam Airlines, China Southern, Korean Air, Cathay Pacific, Thai Airways and Hong Kong Airlines.
The Noi Bai International Airport in Hanoi is the closest. From the airport you would have to get to the main city centre of Hanoi at the Hoan Kiem Lake, from here, a number of shuttle services are available to drop you to Ba Be National Park. It should take you about 5 hours from there to reach the national park.
You can also take a private car transport from one of the tour operators in Hanoi. However, please remember to check the authenticity of the operators.
Overnight trains are available from Hanoi to Lao Cai. From the Lao Cai station, you can avail the services of local taxi operators to reach the tourism centre in Bo Lu Village.