Derryth Bonecloak in the Underdark (Dwarf lady by the Myconids), Cyrel the lass in the back room behind Anders (The Paladins hunting Karlach, provided you haven't killed them), Corsair Greymon in Grymforge (Dwarf guy near the Gnomes) all sell Healing Potions.
If I recall correctly, Lady Esther (Older lady on the way to the Monastery in Mountain Pass) and A'jak'nir Jeera (Armormaster in the Creche) also sell Healing Potions.
Though, Derryth is the best source within Act 1 as she also sells plenty of ingredients so you can make your own potions to boot (Potentially also making stronger variants depending on the ingredients available).
As a note, if your concern is simply the availablilty of potions, vendors restock all non-unique items upon a Long Rest, and if you Long Rest without consuming supplies you can infinitely restock vendors at no cost (Of course, purchasing items will still cost money) so you only really need 1 vendor to purchase all the potions you require.