Any movie with a Will Smith budget is going to have multiple copies of props, some of which may have never even seen the screen. You can't go shooting a movie for $150,000 a day and then send everyone home early because you broke the only fake TG-16 you had so two units seems like a low number. I would assume 4-6.
Regardless, even though this movie stunk this is very cool. Even if you paid a grand for it at least it's actual TG-16 history.