Honestly I just mine them, it really doesn't take too long to gather them yourself, plus each crystal/shard you gather has a chance to give multiple on the next hit and your abilities can gather multiple at a time too. On a few occasions you can get easily u to 7 shards from 1 hit, so unless you need a few thousand shards at any time, just set yourself an half an hour a side to gather a few hundred. Use them, then repeat so it isn't too mind numbing.

Harvesting clusters suck though, they are on timed nodes