Tripod collar mount for Nikon 300mm f/4.5 ED AI-S

I have the above 300mm Nikon lens without the tripod mount collar. Has anyone found a suitable replacement? - I've not been able to locate a Nikon mount as a separate item.

Example image: https://www.kenrockwell.com/nikon/images1/300mm-f45-ed-if/D3R_5353-oblique-1200.jpg

Tom