I've got a dealer license myself... There are insurance companies that deal specifically w/ car dealers. Usually, depending on your state you'll need at least liability insurance and a surety bond. That basic liability coverage doesn't cover any comprehensive stuff (like stolen, wreak cars, etc.), you'll need a full garage policy for that and that shit gets expensive, like $5-25k/yr depending on your location, value of inventory, security, etc.
PM me if you're in FL or GA and I'll recommend my agent.