Nikon has a number to contact them for parts and repairs. You can reach them at these number below. If they do not have the parts, they can direct you to where you can get them:
To purchase a genuine Nikon part, please contact our Parts Department by phone or fax.
Please Note: The Parts Department does not deal with accessories. To purchase a strap, case, cable or other accessory, please visit the Nikon Store
This is for their Sport Optic Department:
Nikon Sport OpticsBinocular & Sport Optics Service841 Apollo Street, Suite 100El Segundo, CANNN-NN-NNNN/p>
Sport Optics Technical Support: 1-800-645-6687.Support is open from 7am-3:30pm Pacific time, Monday-Friday.
I hope this will help you get the part you need.