Alchemy enchants can show up on bracers/gloves/gauntlets, helmets, rings, and necklaces, so you can check for those at all blacksmiths/traders and such.
There are a couple quest rewardsish with Fortify Alchemy enchants, those'd be the closest things to sure things for those.
DARK BROTHERHOOD/MISC. QUEST SPOILERS
Spoiler Frida, the alchemist in Dawnstar, will ask you to find the Ring of Pure Mixtures (Fortify Alchemy 12 pts) in a random dungeon. Once you have the ring, you can hold onto it, or give it to her then pickpocket it back.
In the Dark Brotherhood quest "Mourning Never Comes," if you complete the optional part of the quest and kill Nilsine Shatter-Shield, Miuri will give you Miuri's Ring (Fortify Alchemy 15 pts.)
You can also disenchant the rings to gain the Fortify Alchemy enchantment if you wanna throw it on gear yourself.