I have no idea where "South" is, but if its near Cincinnati, I can recommend "Country Fresh Farm Markets". Three of them in the area. The guy that owns them shops daily in an area near the river where all the produce wholesalers have their warehouses, selling to the grocery chains in the area.
It isn't unusual to find 4 or 5 kinds of lettuce, 5 or 6 apple varieties, etc.
They cater to shoppers that want more variety in produce but don't want to buy a case of lettuce at one time.
Check the Yellow Pages for produce stores, but call first to see if you can purchase in less than case quantities.