The maximum flow rate is written out to DSS even though it is not part of the summary output tables.
You can use DSSVue or you can look at it from the RAS GUI.
Click on the DSS button that is at the top on the far right side of the main RAS window. Click just below the “Part E” and you should get a pull down window. Scroll down and select “MAX FLOW”. For Part C, select “LOCATION-FLOW” and then select and plot as desired.