These items can be purchased at a Farmacia. Tell your guide you need to make a stop there. It is the pharmacy, with green signage, and they can lead you to one. There is one located just across the street from the Vatican, on the south side.
Moleskin helps for blisters. Attach the sticky part to the wound.
Labocaina helps for chafed skin. It is a medicated ointment. Shower and apply before bedtime and even in the morning if necessary.