PHP MAMP user not finding /usr/local/bin
This is most likely an issue with the default search path on MacOS X not including that directory. Homebrew is affected by that as well, so they list a workaround on their FAQ page:

launchctl setenv PATH "/usr/local/bin:$PATH"


That FAQ entry also helpfully references https://stackoverflow.com/questions/135688/setting-environment-variables-in-os-x/5444960 for more details about setting environment in OS X.