Is there a way to add 3D items using just their item ID? I really want to look at some things but only one person owns them and I don't know who it is...

Simple google search.
http://forum.toribash.com/showthread.php?t=492531

I mean items that are already in the game, I was trying to see if I could look at
2115: Muay Thai Left Foot
2116: Muay Thai Right Foot
2117: Muay Thai head band
2118: Muay Thai Left Armband
2119: Muay Thai Right Armband
2120: Muay Thai Left Hand
2121: Muay Thai Right Hand
Edit: a way to find out who owns them might work too.

the item dat in the custom folders lists some obj lines, try messing with that..
other than that, idk..
and just knowing who owns an item doesn't mean they'll have it equipped e.e

Yeh i also wanna see this chrome dome item shmevin owns it i know that hut its in his deac

This tutorial might be what you were looking for.