Another option is looking in peoples houses. If you are not a thief type character many of the people you help allow you to take a range of items from their homes (or shops) and this is not considered stealing. Many of these homes have various items of clothing you can acquire and if you have done a task for them would probably not be considered stealing (as I think you can take items up to a certain value without it being seen a stealing).
For hoods, maybe try the various Jarl Wizards or arcone shops as they might have various mage attire including various hoods.
As mentioned, the thieves guild can also provide. Also maybe Mage/Necromancer lairs or dungeons in general have some items of clothing.