Go to the safari zone in Emerald and go to the southwest corner. Go in the grass with your static pokemon in the lead and run if it is not a pikachu. Even though they are rare static will make it the most common pokemon there. Catch as many pikachu as you can and then collect your light balls! (You can use compoundeyes for the higher light ball % but you will drop it down to rare.)
Hope this helps some light ball hunters out there :)
when i did it i did it without static, the third pikachu i caught had a light ball ^_^..i'm blessed i guess..good advice though. i was planning on using a light balled pikachu in my team for the doubled special attack, but its special attack is kind of appalling..but i didn't ev train it..ha, anyways..