I have been farming with my volcano type lava farm for pirate invasions. But for some reason, I didn't drop after 32 invasions! I this a glitch, or Just HORRIBLE luck?
Well, it's probably that your having bad luck. I would suggest that you stay with your farm, but add water candles. (You can find those in the dungeon). Note it has a 1/2000 chance to drop. Check this link for more info: http://terraria.gamepedia.com/Discount_Card