For some reason I tried to visit the upstream URL for hunspell-yi and found that it is not valid. It looks as if it may have moved to http://www.cs.uky.edu/~raphael/dictionary.cgi though I don't see any link to download the dictionary there.
Pointed the URL to http://extensions.services.openoffice.org/en/project/dict-yi instead as that's more static. See the HACKING/README file in the source for more details, etc.