The larger dealers should have a fleet sales guy who does nothing but that. It's typically a one person job, and they stay in their office most of the time so you have to seek them out.

The normal salesman are easy to spot as they swarm you the moment you enter the parking lot.

Also what you want may exist already, but it maybe at another dealer hours away. The fleet guy can search the inventory and arrange to have a trade made or whatever is needed to get that vehicle brought over in a day or two. If they want the sale they'll do their best to locate it.