Ask B4, i think he has a plug-in of some orcs, not exactly the ones from the lord of the rings i dont think but he used them in a lord of the rings animation he has on this site have alook for it, and have a look at them i think they are quite good
It would be much more realistic if you got an actor to dress up as one. Use some old clothes & tear them up a bit & make them really dirty. For the faces use masks, makeup or add theatrical plaster to change the shape of the actor's head.
It won't look exactly like the orcs in LOTR, but neither do any plugins I've seen. It's too difficult, with the level of detail needed.