If it is perhaps you wish to purchase without any paper trail, then the gun shows would probably be the best place to find larger quantities offered by private gun owners.
If that isn't important, then a site like Gunbroker.com is another option for buying guns both used, and new of any type. One can usually find a local reliable FFL dealer, who will do transfers at a reasonable cost. I've done that here with a local FFL who only charges $20 per transfer. Hope this helps, Mark