if we need something asap and don't have a previously established contact, the last resort is to thumb through the blue book (like the yellow pages but only for construction) and call 3 or 4 companies to get proposals. after chhosing the best company, when the material is delivered see what company is on the side of the truck, or ask the driver where he is coming from, or who he usually delivers for, and call that company directly the next time.
i know it is amazingly simple but it is also amazingly effective at cutting out the middle man. its like buying plants directly from monrovia nursery instead of home depot.
last week we saved about 50%, or $900, on a simple gravel order using this technique.