You will never find a wholesaler, let a lone a dropshipper, for silver bullion. It's not a retail product -- the consumer price fluctuates with the market price of the metal.
If you are looking for a manufacturer of bars ie. you have your own design or want to white label a reputable mint's work, NWTM and several others offer this service for gold, silver and occasionally platinum. But there is no "wholesale silver bar" market per se.