Press Start When Selecting Golfer.
You can get four outfits through the tournaments. And once you beat Louise in Vs. mode you can go back and play over "new" characters which are the same ones before but their fifth outfit. Each golfer is a little tougher than before and the outfits can also be purchased at the store for a lot of money.
-Note- You can also purchase these caddies at the store.
Defeat each character in Vs. Mode to unlock them as playable golfers.