I don't have a mac, and I can't find any tutorials.. but try this?
1. Download/save the items on your mac.
2. locate the downloaded folder.
3. Open it up
4. Locate items.cfg
5. Put the items.cfg into your main FeralHeart folder and replace if it asks you to.
6. Go back to the downloaded folder
7. Everything else in that folder (Textures, materials, items..etc..) need to go into
FeralHeart\Media\Items.
I hope I helped, again I don't have a mac.. if it doesn't work then I'll try explaining another option