Here is what i`m using to get free .edu backlinks. i used to pay
for a service from wf, until i found out that they are doing the same...
opel google and search for: "keyword" "post a comment" or Try this querry in google.

"powered by vbulletin" site:edu
"powered by vbulletin" site:gov

in this way you will get .edu websites where you can post a comment, and from the same niche as yours.

hope somebody find this helpful.