Between my accounts, in the past couple of days, I've killed 3000 blazes by hand with a Looting III sword and received no heads. I've also been asking in chat constantly to buy them, and haven't seen any being sold, nor do I see any on the AH. I've contacted the few people who have gotten past rank 4, and it seems there was some sort of change in the drop rate since they did it. Skillable says a friend of his has killed 100k mobs recently and received no heads. Please look into this as it's the current bottleneck to get from Rank 4 > 5, and to get the next cobblegen upgrade.