There are basically 3 major ways to buy silver bullion; at a coin store, online, and at a show.I've done all three. From a price perspective (price above spot) buying it at a show is cheapest, online is 2nd (if you buy in mass), and buying it at a coin store is most expensive if you buy in small quantities.
Online charges small premiums but you have to pay for shipping and handling. I found that at certain coin shows some dealers charge spot price for silver bullion. I'm thinking they do this for a couple of reasons. For one, a dealer may normally sell numismatics and he may want to try to get rid of his unwanted silver bullion. Secondly, there is competition. If only one dealer charges spot price, then the others find out and they lower their price to match the lowest price. If they do not, buyers will all go to the lowest charger.