Scheduling railing materials and quantities is not an easy task within Revit, you will find related discussions in the dedicated forums. Dynamo could provide a solution but it would probably require some scripting…
The storage type for the rail structure element (red rectangle) is “None”, and so there’s no API access to the underlaying (material) parameter data. Once access is open, a custom node can by written in Python (or C#) to allow Dynamo to manipulate this data.
API material parameter access to the other elements of a rail is available (green rectangle)