In my quest for grease for my recent lens rebuild, I got this response from Nikon Aus:

Thank you for your enquiry.  We are unable to supply lubricating materials outside of Nikon service centres.  We are also unable to provide advice on do it your self repairs.

Subject: Helicoid grease for a 105mm micro Ais

I have an old lens (105mm micro Ais) that works well but has a particularly stiff focus ring, it is not economical for me to send it to Nikon for repair due to the actual low value of the lens, however I have established the problem to be the hardening of the grease on the Helicoid, removing this and applying new grease would appear to solve the problem, however I do not have any of the grease, before taking a guess as what to use I thought it may be possible to purchase this off Nikon Australia or get advice on an acceptable alternative.

So, onto some alternatives, the following sites have discussions detailing the grease used for older Nikkors:

The Classic Camera

and a Telescope Mob

Ice in Space

The main thing I guess is the following seem to be acceptable:

1. White Lithium Grease
2. Silicon Grease