Fred Bauder, 02/09/2010 20:37:

Actually, we could routinely use twitter more, asking for input. With the right searchable keywords we might regularly attract both help with the specific problem and new editors. That could become a regular routine. Obviously asking for help in such a forum could also attract cranks and axe grinders too.

aNobii users helped me to find sources of several quotations on it.wikiquote. I posted requests as a "find the source" contest on biggest single-author groups named after authors with unsourced quotations, but you could also use biggest general groups (which have thousands of members), possibly organizing a contest with their founder, or send private messages to users who have books from that author. I had no time to try this, though.

Nemo