Only have 2 shards left, but I have absolutely no idea where they could be. I've checked every inch of Empire City. They're probably in the most obscure places. I tried printing out a map, but there's no point because i've already found so many, so I can't go around and cross them off the map when i've found them.
My last blast shard was in an easy place, but it is also one place that I would never have looked if it wasn't for luck... it was in the tallest building in historic district near the crater! If you just go around the building without climbing it, it will not show when you push L3. When you are sufficiently high it appears with L3! It's on the very top of that damn building!