No quotes. Here is my logic: Tolkien seems very clear everywhere that Orcs are simply twisted Elves or Men. Taking this into consideration, I would say that yes, Orcs reproduce exactly like Elves and Men do. Considering the fact that we do not know whether orcs were twisted Elves, Men, or both, we cannot decide whether or not they were immortal. I am not aware of anywhere where it is mentioned that Orcs produce faster than the other races, so I would say that they produce exactly like the other races. Perhaps I have missed something. I know, my overview is rather disappointing.