Hi swapnil, welcome.

There are some ways for you to get free domains. You can try a redirection domain, such as www.dot.tk or www.co.cc to redirect to your blog/site or your subdomain if you use free hosting sites that usually give free subdomain to the users. There are also forums that offer domains for posting in their forums such as ddboard and some more.
If you really need free domain go try those one. Hope that will help.