The Tavern Where We Met (OOC)
You haven't IC explored all of the public areas of the keep, but there is a Trader and a Provisioner. Healing potions are not the routine, PHB-equipment list sort of magic item in OD&D that they are in 5e, where anyone with a kit and the right proficiency can make them, however. You would need to find an alchemist who can make them.