i just got my fourth Atma! (Water-bearer) from a seasonal fate, so I agree with hotroderx, hang in there and keep at it, you'll get it eventually, it's a really good feeling after seeing that alert pop up on your screen after working for so long at it.
Also, I think it's more crystallizing the aether that's dispersed when killing the monsters into a physical form, rather than the monsters themselves per se, that's why we can't just get 12 of one kind, cuz they're all different aetherical affinities or some such
