Get a pokemon to use Thief on Red's Pikachu.
Beat Red 3 times,then Red says you are too strong,and he puts ALL of his pokemon including pikachu,into your PC. Then,take the light ball,or take pikachu to the day care. There [=
If you got yellow forest walking path for poke walker and get very very very very lucky you can get it as dowsing item I gotten 3 light balls from it shud work for both versions I actually beaten red while I had a pikachu whit volt tacke in my team epic if you ask me
Look for wild pichu theres a 5% chance you'll find one holding it