GunDealersOnline.com is a directory of licensed gun dealers in the US.
The service is free for searchers, and it’s still in the free trial period for gun dealers, who will have to pay a $5.95 monthly subscription fee. The benefits of using this service are self-evident: you get to see in one same place all the antique and modern gun dealers in your area, browse highlighted offers and even know how much each dealer charges for transfer services, that is: some guns and ammunition online shops ship only to licensed dealers, so the dealer charges the customer a fixed fee or a percentage for transferring the gun. The site also presents lots of useful information to help you determine how old your gun is, where it was manufactured, and how to take care of it. Also take a look at the thorough index of external links to gun industry and fan sites, or become a member and participate in the forums and firearm discussions. 
