Yes you can buy one.
and
Yes, if you buy it out of state it will need to be transfered.
The lower of an AR is "the gun" in the eyes of the law. Everything else for an AR can come to your door when you order it.
Good luck with the build.
Got yourself set on a particular set-up?
I'm looking into another lower, or two. I need them like hole in the head but there are some decent prices coming around again.