Where to get a lens adapter?

I have a Nikon D3100 and my grandpa has an old Nikon camera and a bunch of lenses for it. I was wondering if anyone knew where to get a lens adapter for my camera so I could use the old lenses. If anyone could post a link to a website that sells them or even on the Nikon website if they have them, because if they do, I can't find them.

The wonderful thing about Nikon is that they haven't changed their mount in nearly 60 years. Chances are, the lenses will fit and work perfectly fine- although they might not support metering or autofocus.

In any case, since I don't know what model camera the lenses originally were meant for, or what lenses they are to begin with, here is a Nikon D3100 lens comparability chart

http://imaging.nikon.com/...lity02.htm

A link that will show you all the compatible lenses across the Nikon system since 1959

http://www.kenrockwell.com/...y-lens.htm" class='ext_link'>http://www.kenrockwell.com/...y-lens.htm

If you grandpa's lenses are F-mounts then you can use them right away in manual mode. Just check the link down below. If your grandpa's camera was a much older rangefinder, you're out of luck.

http://www.kenrockwell.com/nikon/compatibility-lens.htm