When i'm about to sleep I just explore in circles and when I wake up in the morning I get about 3 gems, not much but at least it's something
Or how about Gems for Gold? Always seem to have lots of Gold... would be nice to trade Gold (or Grog) for Gems.
I've gotten quite many gems from exploring the map. And i think I got like 100 gems for only getting to 200 PR. Do some questing and you will get your gems