There is a Walgreens fairly close to downtown Disney. You go out of the Disney area and take a left onto S. Apopka Vineland. The Walgreens will be down the street on the left hand side of the road. The address is:
12100 S Apopka Vineland Rd
Lake Buena Vista, FL 32836
They have a 24 hour pharmacy. The pharmacy phone number is (407)238-0600. You probably would want to call ahead to make sure they had the medication on hand.