Hello Ramesh,
I was also trying to find out similar kind of information on microncontrollers around 10 years ago, when I wanted to jump from the Z80, with the help of a friend who was working in BHEL I decided on the 8051 and now I realize that, that was the best thing to do.
If you take the market (Bangalore) as an indicator the 8051/52 are the ones which sell in much higher volumes than other micros. The most populer '51s are 89C51,
89C2051, 89C52, 89C55, and 89C51RD2.

Recently many Indian companies have changed over to Cygnal, I think more than 50 to 100 kits have been sold in India, you can contact M/s Hynetic, Bangalore , they will be able to give you precise figures.

For information of 89C51/52 contact M/s Oriole, Mumbai or Bangalore.

The above companies may not give you actual names of companies using the 8051, but you will get the idea of how many are basing their projects on 8051, if that is the information you want.

Hope this helps.

Regards,
John.