There are seven different types of Iso-8. Below are the main places you can get each type.
Yellow, White: Collecting stars.
Red, Green, Blue: Getting a Tsum Tsum that you already have from an Orb Box. You can also get them from Daily Battles.
Pink, Violet: Getting them from Battles. You can also get them from various events.
Getting a Tsum Tsum that you already have from a Coin Box will yield a Yellow or White Iso-8.