Manheim offers floorplan financing through Manheim Auto Financial Services and you can find information at any Manheim Auction. Their rates and terms are pretty good compared to AFC and DSC.
Auto Use is another floorplan company out there nationally, although we don't use them.
There are smaller regional floorplan companies available, just do a Google search for used car dealer floorplan and you'll find some that way.
What state are you in?