Where can iPhoto '11 be downloaded?
...and, I'm answering my own question.  Apparently (this comes as a surprise) the entire iLife '11 DVD is available as an ISO from archive.org (https://archive.org/details/iLife_Install_DVD_Version_11_2Z691-6677-A_Apple_2010).  I'm not sure whether that's legal or not -- I would expect archive.org to be careful about clearing copyright before hosting uploaded disk images, but maybe not.  If this is considered software piracy then please feel free to delete this answer.