1- Idk sorry
2- You can rarely found them through gather, buy 1%, 2% and 3% gifts with Life Crystal or Bond Crystals and 3% gifts with Whale Medals. And you can also get bronze and silver medals with forging or during login campaign or DMM gifts. And... that's all. I guess.
3- Rates are the same yes. It's high but we get tons of Nazuna cake anyway.