I know it's really hard and difficult but anyone can help me to get backlinks from this site. Thanks in advance. I really appreciate if someone help me in it.
Unfortunately it is virtually impossible, if your site is a non profit organization you may have a chance, its worth a try. I will say though every .gov site I have ever contacted has at least bothered to reply with a no instead of not replying at all.
The easiest way to get .gov and .edu backlinks is to use Google to your advantage. I personally use scrapebox to find good links, but you can do it manually. Find a CMS platform such as blogengine, wordpress, drupal, joomla and look for "tags" or "keywords" that can be found on all pages that contain these CMS platforms. For instance: inurl:.aspx "Add a comment" + "Register to post" + "powered by ...." etc. Go into google and use search strings to find these blogs that have dofollow and post your link on them. I would however suggest that you only post links on sites relevant to your niche. I would also not post links on sites that have 2,0000 spam links either.