Yea for some reason one was never put back on after I got rearended. Is it against the law to not have one?

Anyway id like to purchase the license plate light for my car, and was wondering how difficult do you think it is to put in? When I look above my license plate I see a cutout to what looks like the lights are suppose to go, and I also see a plug (guess that hooks in the light assembly). Does anyone know a site where I can buy that at? Im not sure what exactly to look for, so any help would be great. Btw I drive a 98 accord v6 coupe.