the chainhooks from the undersides of venoms/raiders? (don't remember which one has that bit)
Aside from that, there's nets in the Night goblin boxes, or you could try making them out of wire(wouldn't reccomend this)
Selling/tradings tons of GW stuff, check the Slave Pits in the Barter Room.
Captured Victims: Castellan Crowe, Ultramarine Chapter Master