Gun shows, Auctionarms.com, and Gun Brokers.com. The gun shows tend to be a little on the high side, but good deals CAN be found on the auction sites. Over the past few years I have purchased a large number of gun from the internet sellers. If you are not in a hurry, try this.
In well over twenty five gun purchases, I have only bought one that was not up to my expectations. The dealer readily took it back, paid all postage, and gave me a full refund. I am sure there are those that will take advantage of you, but most provide a three day inspection period, and will accept a return brought to their knowledge during that period.