The problem with any OEM Nikon parts is that you have to be a Nikon Service Center to get them. Nikon no longer ships replacement parts to dealers or camera repair shops.
In your case, that isn't as terrible as it may sound. The parts you are looking for are generally called split rings. On most cameras they are round. A few camera straps, like this one, come with round split rings attached.
A while back Fuji used some similar triangular rings that caused excessive wear to the lugs on the X100 and X-Pro1. Once the lugs break off the entire back on the Fuji models must be replaced. It is also possible the lugs were made out of too soft of a material. Link
My suggestion would be to go to a sporting goods store that caters to fishing lure builders, as split rings of various sizes are used for building certain types of lures. They usually also sell some specialized pliers to open them when installing and removing them.