make a folder on your harddisk called 'pd-externals' or something.
in the taskbar of pd, go into preferences->path….there will be no
space to add a new path, but you can do it this way: on an existing line, without adding any spaces, add a colon and then the path to 'pd-externals'
so, for example, /System/Library/Fonts will become /System/Library/Fonts:/pd-externals
apply and save these settings, and your externals will work.
if you have subfolders within your externals folder, then you will need to add separate paths to each of these subfolders too.