There is a website, I think it's called autotransport reviews. They list hundreds of carriers. Two things I can tell you based on my experience-NO advantage to book more than 2-3 weeks out; that's when they start lining up their loads; sometimes the people who review get paid (so beware). I used reverse psychology - I found a shipper from the east coast -near my destination- who was delivering to the west coast. After all, he was headed home anyway!
It seemed to me that MOST of the carriers were actually just brokers; that is you called them, they went on the internet checking their suppliers, got a price and added $$$ to it. Good money if you can get it. My delivery was flawless.