Just stumbled upon this nunchaku thread. Or "nunchuks" as they are so often called. I have been working out with them since I was a young teenager (and suffice to say that was quite a long time ago).
On obtaining them- professionally made ones are nice but don't be dependent on it because if you have access to tools they are so easy to make yourself. Regarding whether they are legal to carry or not, it varies state to state. In my area as far as I can tell the law seems to say that you can carry them as long as they're not concealed, and martial arts schools here have no problem teaching their use to kids.
Some cautions- All the super fancy Bruce Lee twirling moves you can do with nunchuks are a lot of fun once you master them and quite impressive to demonstrate, but in a fight they are for intimidation only, something to convince your opponent to keep his distance. If that doesn't work and an actual fight begins, nunchuks are for winding up and delivering extremely powerful blows, up to 1600 pounds of force applied to the target, which can easily break bones or cause major head trauma. If you're not careful you could easily kill someone with this weapon, so keep that in mind. Of course they are also useful in ensnaring a person's limbs with the cord or chain between the sticks, or in choke holds, but those moves are a bit more intricate than just swinging away at someone. Personally, I carry nunchuks when I go out on patrol and I hope I never have to actually use them. I also carry a taser, a non-lethal weapon which I would much prefer.