This isn't really an answer, but maybe it will help. I found that the Source is included in the International Index to Music Periodicals, an online database to which many university libraries subscribe. However, the actual text of the articles with the "Power 30" lists are not included. However, it might be possible to get the articles from your local library's Interlibrary Loan service. I can give you the citations for the issues and page numbers of the relevant issues if that would be helpful.

Here is one partial affirmative answer: Jay-Z topped the list in 2009. See http://power30.thesource.com/.