There is no graymold salve potion for sale. Graymold Herbs are sold by Harmon in Lost Isle and Mundt in Lorelei. They can also be found laying around in multiple places.
You can find Cleansing Powder in places Tower of Magi, Slime Pit, Filth Factory, Woodsy Tower. It is also sold by Anama shop near House on the Hill area (although you need to be a Anama member to access that shop), McElton in Greendale and Shane in Blackcrag Fortress (if you want to get ripped off).
You can also find an Aescal's Ring in the Tower of Magi and Drake Aerie for unlimited disease heal (nvm, it seems this item is bugged).
