I have a pair of these levers on my bike and I flipped the bike over to do some work on it. A kid in my building squeezed the brake lever and a round spring rolled out and away into a storm drain. My front brake no longer works. The levers are pretty expensive so I'd really rather try to replace the spring instead of the levers, does anyone have an idea where I could find that part? There are two springs in the brakes, one that is a circle with two lengths of metal coming off and one that looks like a traditional coil spring, and the coil spring one is the one that rolled away.

That spring in the brake lever is just an assist and isn't essential for the brake to operate properly. If the caliper itself operates smoothly and its spring tension is adequate, that's sufficient. You might be able to find a suitable diameter coil spring at a hardware store and perhaps cut it to the right length.