In Baldur's Gate: Enhanced Edition it is sold by Thalantyr the Conjurer in High Hedge.
In Baldur's Gate II it is added by the expansion Throne of Bhaal. There is one for sale at Arcana Archives and Karthis al-Hezzar. Sister Garlena also sells one at Watcher's Keep, and the temple of Waukeen sells one in Amkethran.
|“||Typically carried by travelling healers, this leather case folds open and allows the user to strap delicate potion bottles to its cushioned side with numerous leather thongs for safe storage during travel||”|