I lost the little rubber ring that sits at the base of my shift knob
 

No you're not allowed to ask how this happened because I'm not really sure. I probably dropped it when I was installing my gt-r start button but whatever.
I suppose it could still be in the car somewhere but at this point it is a mystery.

Where can I get another one? I don't even know how to articulate what it is i'm looking for enough to search for one.

Spacer? Base? Rubber thing you screw the shift knob down onto that keeps the leather from bunching up?

you running nismo knob? those are nearly impossible to find. get a flash light and find it. probably under your seat.

Yeah haha of course they are. Blargh.

It had somehow rolled under my passenger seat and was stuck between the seat bar and my amp.

Woot.

Not sure if this is what you are looking for:-

2012 Nissan 370z Coupe OEM Parts - The Nismo Shop

You can search this link if it's not the exact missing part you seek.