Yoshi said, zodiac weapons are absolute. It's guranteed to be 2nd powerful weapon in the game. Just because of that reason, it's set to be hard to get. However, according to yoshida himself.. they might make it easier to get near future, but not in 3.0. This is just an advice, but don't farm atma's 2 - 3 hours straight, no matter how hard you want to get it. It won't happen so easily. Try changing areas every 40 min or so. Sometimes, give it a rest. There is something about the time.. not just pure drop rates. I might sound crazy, but I got all 12 within 6 hours. But, took me 9 days. While I can't get single atma on my dragoon playing 3 hours straight.