I need a large intelligence potion to craft a potion of authority. I've been checking the merchants who carry potions every hour, but so far they only carry medium intelligence potions. What level do characters need to be before merchants carry the large version?
Alternatively, is there any location in Act II where a large intelligence potion can be found?
Failing all that, is there any way to raise persuasion other than +1 amulets and the potion of authority?