Games : How to randomly generate ores

I have a superflat world, where I have some pretty big structures. I didn't think ahead when I was creating the preset, so there are no ores anywhere. I came up with the idea to (in creative) put down some command blocks that randomly generate random ores in a small location. Problem: I suck at command blocks. Anyone know if there's a code I can use to do this, if it can be done?