You can simply glue a ball bearing inside the flag pivot and face the end of the rod flat, and polish. Then again, very little of the friction we deal with in the flag pivot actually comes from the end of the pin/pivot. By far, most comes from side load, particularly on large diameter pins such as 1/4". Lots of people feel like they can simply balance the flag perfectly and do away with most of the side load. Truth is, that load varies with wind speed and flag design. What's balanced in a static state is not when it starts moving or wind force is applied.
That's why I prefer smaller pins and teflon pivot material on my flags. Side load is inevitable. I think we just have to deal with it as best we can.
I've seen ss rods that were pretty badly scoured by the flag pivot...likely from dirt or some abrasive getting inside. For that reason, I think brass would be less than ideal.