Used parts! Junkyards, eBay, whatever. Odds are you’ll be able to find a replacement unless the factory knob was super fragile or your vehicle is exceedingly rare.

If your vehicle is vaguely popular it’ll probably have a stl (think exported 3D shape) available. In that case I’ll print/mail you one assuming you’re in the US. If you’re not in the US hop over to [email protected] and I’m sure someone will help you out.