IB has DIA options. Enter DIA (or DJX for index option) in the underlying. Select option (equity or index), and choose the month of your choice. IB should give you the list of options with different strikes. Select the one that you are interested. Normally you don't have to know the symbols of the options. You can also use optionTrader toolkit in IB. View the webinars from IB and learn how to use options with TWS.