Have you pulled off the igniter knob to see if the inside part is broken? It should just pull straight off; pull towards you. If it's just spinning on the igniter then I'll bet the plastic seat on the inside is cracked or broken.
You might check locally at an appliance parts store (Sears Parts Store might have it). If not, go to
Appliance Parts Pros.com Discount Appliance Parts – Since 1999 and look up your range model number. They will have a diagram that shows your range and associated knob.