Cut the pork tenderloin into 1/2"-3/4" medallions and place inside a zip top plastic bag one at a time. Pound with a rolling pin until the medallion is 1/4" in thickness. Repeat with remaining medallions.
In a large skillet, add enough oil to cover the bottom of the pan and heat over medium high heat.
While oil is heating, add flour, salt and pepper to a 9" by 13" baking dish. Dredge pork medallions in flour mixture and place in the hot oil. Brown on both sides and remove from pan. Keep cooked medallions warm in the oven while preparing cherry sauce.
Add the cherry juice and vinegar to the skillet, stirring constantly and loosening up the bits on the bottom of the pan. Add brown sugar, dry mustard and salt and pepper to taste. Cook until slightly thickened. Add butter and stir until melted. Toss in fresh cherries and serve with fried pork medallions.