In route 115

First go to Mauville City and go up use HM03 Surf and go until you find land .Not were you enter Meteor Falls! You will find alot of trees and 2 trainers .Go into the grass and you will find Jiggleypuff. You mite not find it the first time. So keep looking .Faint all the pokemon until you find it.

Go to Rustburo and go up you will see a bunch of ledges. Then go surf you'll see a girl on an island. Then keep going you'll hit land, where there will be a couple of trainers, there is a small patch of grass, search and you'll eventually fing a Jigglypuff. Keep looking, you'll eventually find one (trust me it took me like forever).

trade frome fire red or leaf green

2 pokemon i found

go up from rustboro to route 115 then go neier the island find a place wer u surf and keep going untill u see trainers on land there will be jiglypuffs there. but i if there is not will srry because i read it online