Cows is probably still your best bet for finding Azathoth Organs.
I rarely find them anywhere else myself, but I never look for organs really.
And I've heard a few people saying they think Alkor's Shruken Head's drop rate was lowered.
So I'm assuming from all the talk about it, that yes it must've been lowered.
But I could be wrong, everyone might just be having a lot of bad luck.