Trying to figure out why some potions show up in "Magic" tab but not formula book

[Daggaroth]

Hi all,

I'm playing as an Alchemist in my campaign and so I have been getting used to the creation of potions and I wanted to make a "potion of magic fang" but that particular potion doesn't show up as an available formula when I go try and find a source for it. There are a few others in there like "magic weapon" also show up in the "magic" tab but not in the formula list. I am wondering what I am missing here and how do I go about getting access to making these items. Any assistance in this would be greatly appreciated!