supplier not releasing Bill of Lading

Are you saying you dont have the BOL for the first container, but you have already paid for it?

Where is it coming from?
If its being imported from overseas, then you might be able to get it from the customs broker.
That is the person that will be responsible for the container clearing customs.

You might be able to get it from the ship lines carrying it (if its on a ship).
But either way, DO NOT accept it without a bill of lading.
Once you do, you are responsible for whatever is in it.

Also, DO NOT make payment on the 2nd container before you get the BOL for the first one.

Never mind the containers - what was the ORDER?

If your order arrives in two containers, it is still ONE order and payment should be made on the complete order.

Your post is a little confusing.

Sometimes second shipping orders will not even be sent until the first shipping order has been paid. This is pretty standard.