Just pick up some cheap sprint spikes at eastbay.com or your local running store. When you are sprinting, you should be on the balls of your feet, so your having flat feet won’t matter. There won’t be a “heel to toe” transition, so you won’t have much of a chance to pronate or supinate. You will not want to wear your orthotics (you probably couldn’t fit them into spikes anyway). Check the surface of the track to see how long your spikes should be, and also whether you need to get shoes with a hard spike plate or soft spike plate (some tracks are just asphalt, so you would want to get spikes with a soft spike plate, or even lightweight trainers for more cushioning).
So you say not to even bother with putting my orthotics in running shoes. And about the spike thing, does that really make a difference having them instead of just basic running shoes? Concerning spikes, should they be used outside of a track setting like when I’m at home and on the open road? Just curious.
You don’t have to get spikes. They are just cheaper and better for sprinting short distances than normal shoes and I assumed you would be doing most of your work on the track. If you want shoes that work at home too, look into any lightweight trainer. The forefoot of the shoes can have a little cushion, but you don’t want the shoe to have a big, cushy heel (a la Nike Shox) because it will mess up your sprinting form. Nike Free’s would probably work well for you as a sprinting shoe since you are almost 200 pounds. The only time I would worry about putting in your orthotics is if in the longer sprints your heel starts hitting the ground. Are you thinking of 100m or 200m sprints or something longer?