Try this footprint - inurl: "node" + intext: "login or register to post comments". Save your google search setting to 100 results per page. You can install SEOQuake toolbar to check pagerank. Dofollow lists are no wander with this type of footprints though it takes a lot of time to arrange a good and long list.
Try DoFollowDiver, all you have to do is enter keyword and hit search, you will be given a list of blogs that are do follow and that you can comment on. Do remember that your comment should be relevant, give great content, and not be spammy... Talk Soon Joe