Try the Pro Desk at Home Depot. The folks there have access to what they call the Bid Room. Large potential purchases like yours are given to the Home Depot regional buying office. They, in turn, contact the manufacturers / distributors for better pricing. The savings are then passed along to the customer. If they won't help you ask to speak with a manager.

Charles, you have a huge potential order and anyone in the building materials sales business would kill for it! If one of my guys refused to work with you on an order of this size I'd fire him!