I simple way to find .edu and .gov blogs to get backlinks is to simply use the following search format: site:.edu YOURKEYWORD “post comment” -"comments closed" -"you must be" site:.gov YOURKEYWORD “post comment” -"comments closed" -"you must be"
Its best if you comment in High PR website but you have to see the OBL as well. Because nowadays there are many spam comments in High pr blogs too.
Best way I've found is to find out what .edu links your competitors are using. Then contact those sites and get a similar link.
Link from blog commenting are not valuable at all, it will flag your site for low quality backlinks. On the other hand one good quality contextual link from related theme based website will do fortunes for your site. Having most of the links from low quality sources will adversely effect your website and rankings. I will take a single contextual back-link from relative site then 1000's of So Called HIGH PR COMMENT links. Do ethical link building and provide some value to the visitors, by following this your site will survive decades. Build your BUSINESS, Don't Destroy IT.
I feel best to avoid commenting sources, if you're able to get links from commenting then the chances are the others can do it as well. From what I've seen in the last few months, Google have devalued the comment links. They even count a website as low quality if high proportion of the backlink is coming from low quality resources. Doesn't makes sense to get commenting links to me.