I think it is p/n HN-1 Screw in Product # 508 NCP. \
Also fits PC 35/2.8, AF 24/2.8D, 20-60 1x nikor.
I got this in my Nikon product Guide 1999.
I would call Nikon Parts.
My son needed to replace a part in an underwater housing.
He was calling it seems everybody in Florida to no avail.
I said call the manufacturer- well he finally did and they shipped it via air that afternoon.
If I am not mistaken this lens requires the HN-1 hood.
Here is a link of a good old used equipment store in Calgary, Canada (Nikon section - scroll down and you will see that they have a HN-1 for sale): http://www.vintagevisuals.com/nikon.htm . I have personally been at their store and vouch for them being genuine. Should be easy to get it up to MI, I guess.
I hope this helps, best of luck.