How do I find call for papers for special issues? I found that announcements of special issues for many journals are quite hidden. Often the calls are not even visible on the journal's homepage.
What is the best way to find call for papers for special issues?

I hope the rejection rates are lower there, but I've also heard that special issues are sometimes for friends of the editor to get their stuff published.
Subscribe to different publishers' mailing list specifying you'd like to receive call for papers in your field, and chances are the publishers will be more than happy to send them to you when they come. That's likely to be more efficient than trawling the target journals' website every day looking for call for papers.