There’s still a large percentage of people—even experts—who aren’t at those sites or who don’t know how to get good search engine ranking.
Check out this treasure trove of sources just waiting to be tapped: At the article directory sites.
Sites like EzineArticles.com, ArticleBase, ArticleDashboard and Expertclick: the Online Yearbook of Experts, have thousands of experts who would probably love an invitation. And most of them can be found fairly quickly because these sites are usually searchable by category.