How do I as an agent register with the banks to list their REO properties?

The real estate laws in your state, for example in my state a agent can not work by thierself but have to work for a broker, So you would get listings for your broker.

But some banks have their own real estate people that work for them, others have contracts with brokers to represent them. So you would have to talk to the manager of that department as to when and how they allow such agreements. Different banks will have their own various rules