Instructions
Travel to Fuschia City and then head to the Safari Zone entrance. Afterwards, pay the $500 fee to enter the zone.
Head towards Safari Zone Area 2. Once you have arrived, simply spin in place in order to encounter wild Pokemon but not reduce a single point from your step counter.
Continue to spin in place until you encounter Kangaskhan. If you do not encounter him, flee or throw rocks at other Pokemon to force them to run away from battle.
Throw as many of your Safari Balls as you can at Kangaskhan until it is captured. You can throw rocks at it to increase the capture rate, but you will also increase its chance to flee from the fight. Alternatively, you can use bait to decrease its chance to run away, but you will also decrease your chance to capture it.