This sort of thing needs to be shown on the blackout pages, so people can easily do something (call to action) instead of just leaving the page.
Great job with the widget, it shows all of my reps and the calling works. To answer your question, being on the front page of HN should help. Have you tried the relevant subreddits (r/sopa, r/politics, etc)? Reaching out to Wikipedia, reddit, etc directly?
Have you thought about making this more generic, and/or letting people customize instances of it, so that it can be used for other issues?
We created it as a generic, customizable widget for activists. Anyone could add talking points, a title, etc. We also have a way to browse through the widgets that other people have created. (Although since we made it at a hackathon this weekend, there's not much there.)
We made the SOPA widget and page AFTER the hackathon was done, because we realized it was an ideal use case.