Back links the more in number the better similarly if a site can get back links from .edu or .gov then it can upgrade the authenticity and value attached to your site. But getting a .edu and .gov link is even more difficult as these sites are focused on education, information and government policies and are most unlikely to sell or exchange links. Unless some site decides to donate a few links.
But the question arises then how can one get links from these domains. The things that can be tried are
Firstly try getting a .edu blog of your own as few .edu sites sell .edu blogs to anyone who pays their monthly subscription. So if you can afford a high subscription or if you can also sell a few links from your .edu blog and earn the invested amount then it can be beneficial as you can point links from it to your site.
Secondly one can get links by posting comments on the various.edu blogs which are mainly made by students. The .edu sites generally have blogs written by its alumni and its students and one can post links in form of comments. But while posting comments one must be sure that the comments and the links should be in relevant post and the blog should not be spammed by irrelevant and unrelated comments.
So go ahead and start getting .edu/.gov links and yeah do let me know if you find some good source by putting them in the comments so others can benefit from the source.