Where can you get replacement spikes for your high jump shoes?

You should be able to get them at any sporting goods store. Probably you want 3/8" spikes, because on most high jump shoes the spikes are recessed into the platform-like bottom of the shoe. You'd probably trip if they were longer and you wouldn't want anything longer than that on any decent high jump surface. Make sure you put the heel spikes in, because they help you get a more secure plant when you take off. Take it from a 7'1" high jumper-just so you know your source is credible.