First of all go to Digg and signup for an account and scroll back to the older stories relevant to your niche. Diggs that have been dugg like more than a year ago or older. Click on the comments section for any digg post that has less than 30 comments.
Use a pagerank checker to check the pagerank(Older posts usually have a higher pagerank).
Post a comment and put one of the links in the comment.
Now you have a high pagerank dofollow link.