Any tricks you can share on how to find CPU's loading with my customer?

Thanks - I have a lot to learn and appreciate your help.
I am trying to establish new carrier partners for some ongoing business in a number of locations. I am bringing in raw material. I want to know who is transporting product from the manufacturing site, so I can see if they'd be interested in hauling my loads. Are there any tricks to finding out what carriers are coming out of a plant or what CPU's are picking up?