Pottermore Potions Tip: Do not buy mistletoe berries either!
So far it seems as if this applies to every ingredient but I’ll still update y’all. When you run out of mistletoe berries you can go to book 1, chapter 12, moment 2 and get them for free. Zoom into the third layer and scroll next to the tree and you should be able to collect it.
So, so far this rule works for Bezoars and Mistletoe Berries. I’m pretty sure it applies to every other ingredient. I’ll update this so that you don’t have to search for it you can just go to the correct moment and location to obtain whichever ingredient.