Here is a product for removing mold on leather.
http://www.topoftheline.com/
We used to use alcohol to kill fungi (yeasts and molds are both technically fungi) on agar plates in the lab but it may dry leather too much.(Concerned about allergens such as Aspergillus fumigatus, we were isolating these fungi from the air so some species must have been similar to those invading leather.) You can sometimes kill mold without getting rid of 100% of the stains.
Mark Cutrufelli
Laurel,MD USA