If you have access to a university library that has subscriptions to various historical databases, see if they have access to the Chadwyck-Healey African American Biographical dB (through ProQuest). William Still's book has been digitized by this group and can be searched for all entries relating to Rochester.

I've done a full text search for all entries relating to Norfolk, VA and was quite pleased with the results. I'm not certain if Still's book is available elsewhere electronically.
The original book has a table of contents but not an index which makes the dB especially useful to researchers searching for specific names or localities.

Below is a link to their web page explaining the contents of the dB.

If you live anywhere near Washington, DC, or plan to visit soon, you can access this dB free of charge at the Library of Congress through their electronic database access services. You can only access this on-site, not via their web page.