FFL = Federal Firearms License. You'll need to have a local FFL send a signed copy of their paperwork to the person/place you buy your 6400c from. Then the rifle will be shipped the the FFL, you go there, fill out the Fed/State paperwork, perform a quick background check and pay them a fee ($10-$50). Then you go home with your new black beauty
As for an online dealer, check with www.sawlesales.com
. They have 18 in stock and are asking $985.17. Also, IM or email "ArmyInf" here on the boards. I picked mine up from him for $967 shipped!
As for EOTechs, tactical slings and lights I recommend C4iGrant @ G&R Tactical
. He has great prices, carries great products, has excellent feedback on the EE and is one heck of a nice guy
Oh yeah, he's also a site dealer and I always like to help those that help this site. Be sure to check out his forum if you have any questions.