you can update the xml files in /Applications/darktable.app/Contents/Resources/share/lensfun/version_1
since the lensfun database is updated when creating an application package you can extract a quite recent database from my packages in current OSX Build - #66 by MStraeten
to do it manually you need to install lensfun via macports and then run lensfun-update-data and then copy the updated files into darktable.app