You can find garlic in The Elder Scrolls IV: Oblivion primarily as "Garlic Clusters" hanging in basements and certain buildings, especially in the city of Skingrad. Here are the best locations to find garlic:

• Skingrad :
  • In the basement of the Mages Guild.
  • By the fireplace of the Fighters Guild.
  • In the basement of Rosethorn Hall.
  • Four garlic clusters in the basement of Summitmist Manor.
  • Two clusters hanging in the Grateful Pass Stables outside Skingrad.
  • Lazare Milvan's house basement contains four garlic clusters (note: entering the basement is trespassing)

• Weynon Priory :
  • Six garlic cloves can be found here: three cloves in a bowl on Jauffre's desk upstairs, and three more in a bowl on a bookshelf across from the desk. This is a convenient early-game location to gather garlic for the vampirism cure quest without trespassing

• Other locations :
  • Garlic can also be found in various houses' basements across Cyrodiil, such as Glarthir's basement in Skingrad (four clusters), and some stables and trader houses

Garlic harvesting is never considered stealing, even if done openly in front of owners

. For the vampirism cure quest, you need six garlic cloves, which can be collected conveniently from Weynon Priory or combined with garlic from Lazare Milvan's basement in Skingrad for a total of ten cloves

. In summary, the best places to find garlic in Oblivion are Weynon Priory (safe, early-game location) and various basements in Skingrad, especially Lazare Milvan's house and the Mages and Fighters Guilds