Use boot camp and try to make one or search around for a simba/scar pk script.
Heres a clip of using simba based auto switcher:
[YOUTUBE]vkBvR1EQfWI[/YOUTUBE]
EDIT: Note, jagex prevents bots switching more than 2 items at beyond human speed by making it "lag". So if you were to make one, you gotta slow it down a bit.