I have significant experience in the books and media niche, and can assure you that you are going to be hard pressed to find any suppliers of current, up to date bestsellers who dropship. Older books will be available generally, but not at great margins -- the standard wholesale book rate is 55% of cover price, and as you might notice most retailers sell for just barely over this. Older books, or ones just off the NYT list can be found where they were dumped to overstock operations, who in turn sell them to dropship companies and the like, but even then margins will be slim.
Be very wary of any company offering to sell you something like Chasing Fire
at a price on which you can turn a profit; the incentive to dropship an in-demand item just isn't there when they can sell it themselves for whatever you can, and the wholesale price is the same whether you're buying one pallet or ten thousand pallets of the book from the publisher.
"Failure is not when you fall down. Failure is when you don't get back up."