Most of the bigger plywood companies in India, also manufacture blockboards.
Here's a list of some of the blockboard manufacturers in India.
Century Ply - Manufactures block boards in both the MR and BWP grades.
Kitply - It's block boards are branded as Kitboard, Kitboard Gold, Swastik Commercial MR grade.
Greenply - Makes blockboards in both internal and external grades.
There are also several other reputed plywood and blockboard brands in India, other than the ones listed above.
In India, blockboards are usually available in two different grades.
1. Interior MR grade
2. BWP Exterior grade.
Interior MR grade blockboards are moisture resistant, but cannot be said to be waterproof. The BWP (Boiling Water Proof) exterior grade block boards on the other hand, are of waterproof grade, and are suitable for interior as well as exterior use.
The Indian Standards quality specification for blockboards in detailed in document IS:1659
When to choose blockboard over plywood?
Blockboards are the preferred choice of material for any furniture that requires lengthy pieces of board. For example the doors of wardrobes, shelves of a book-shelf, and any such pieces of wood longer than 7 feet are usually made using blockboard instead of plywood.
The reason for this is that lengthy pieces of plywood are likely to bend at the center, while the different composition of the blockboard makes it is much better in this regard. However for shorter length pieces, plywood is better.