I can find Mobil 1 AFE 0W-30 anywhere, anytime of the week around here. Only from M1, though.
Like the others have said, probably because there's not big demand for it I'd assume. Is there any manufacturers that recommend a 0W-30 on a new car? But, it's definitely not hard to find if you're set with Mobil 1, I've never seen Castrol, Pennzoil, Valvoline, etc in that flavor on store shelves as of yet. I've heard that Autozone carries 0W-30 Castrol Edge, but, each time I've been to an AZ, I've never found it.