You might want to find an old copy of "Lives of the Artists" by Vasari.....a
listing of the various Renaissance artists(Michaelangelo, Leonardo,
Donatello, etc...) of his day and comments and quotes from them, as well as
Vasaris' critical and historical slant. Fascinating reading. The much
aforementioned "Annotated Mona Lisa" has many artists quotes, and you might
also try digging up old calendar books and such that feature single
artists...they often have many quotes as well.
Have a good summer!