if it's one of those one-click installers that you used, you need to right click (ctrl click) on the pd icon, and choose 'show package contents' ....and inside there somewhere you'll find the 'extra' folder. put your .pd_darwin files in there
When i use ctrl-click on my pd icon i open the package contents and appear:
info.plist
MacOS: -pd.command -pd.term -PureData
Resources: -pd-file.icns -pd.icns
Where is the extra folder? Maybe i should download another compilation...