There is a glitch where you can get 2 every 3 weeks. The week before the strongest curse week, pick up the weekly bounty from Petra, and complete it. Turn it in and get the item to activate the Oracle. Then get on before reset, and go to the Oracle. A few minutes before reset, summon the chest, DO NOT OPEN THE CHEST. Wait until the weekly reset (you will know when a new adventure notification pops up on your screen), then open the chest. You should get a lore card, then do the Petra and get the bounty and do it again, getting 2 every 3 weeks. Obviously if you haven't started yet, you won't be able to do it, but this will get you a couple extra ones if you need them. Here is a video that explains it as well https://youtu.be/7AoxLs89uiM