Hi, and welcome!
If you are talking about the plastic retention plugs that are used on various panels under and around your vehicle, they can be purchased from any local parts store, or off ebay if you have a week or so to wait for them to arrive. There are multiple sizes (diameter and length), so I would recommend pulling one of the retainers you have and measuring it or call your local Infiniti/Nissan dealer to get the OEM part number.
Example pic attached for your ref.