Check for local steel suppliers. Any good size city will have a couple. You will likely save on shipping and may save on drops.
Dura-Bar has a supplier finder. Dura-bar being a well known cast iron supplier. There are of course other suppliers.
Depending upon your needs a local foundry might be able to fix you up. You have to find one of course which in this day and age is no sweet adventure.
MSC and Mc Master are of course national but do look for similar local shops.