Most good rock sources are not public knowledge. If they were, the best rock would be gone pretty quick from that spot.

We all ruin good rock, even experienced knappers. But that shouldn't discourage you. Try to get the best rock you can. It will save you a lot of frustration, believe me. For example, you wouldn't buy crappy arrows to practice with just because you might loose them, would you?
Glass from wine bottles is a good alternative to stone. Knap the darker colors: it's easier to see the flake scars.