Title says all. Are there any, other than the 3 day respawn barrels in the market district?

You could get your inner thielf on and just go on a crime spree at night. Just be careful - but anything you find that can go into a potion, the steal tag will disappear when it is used in alchemy or whatever.

That wouldn't fit with my role play, but thanks for the suggestion.

http://images.uesp.net/d/d5/OB_Flora_Fly_Amanita.jpg are abundant in and around the IC.
If you have access to the Arcane University, there is a wide variety of plants just outside the alchemist's shop (door, furthest right).
A Hestra Rune stone in the middle of the northwestern peninsula of the IC Isle has some plants growing around it.
Other than that, boar & crab meat?

Also, check in the moats adjacent to the inner gates. There are Lotus plants there.