There is a Jorg Sprave video in which he launches a golf ball quite a ways. He used very heavy bands. Some of the distance is a function of the spin which a club imparts - it is impossible to duplicate this w/ a slingshot. As mentioned, shepherd’s slings are a better way of launching a golf ball - but, requires some amount of practice And you really should perfect your technique w/ a rolled-up sock before trying a tennis ball before trying a golf ball.
There is also something called a fling stick which is like a lacrosse stick for golf balls.
Can I ask why you are interested In using a slingshot for golf balls? I have fooled around w/ alternate golf ball launchers for years and may be able to help.