Under federal law, the interstate sale of long guns is legal in face to face transactions. It was made allowable nationwide by the FOPA 1986. Prior to that it could only be done in contiguous states. The interstate sale of handguns is prohibited. It does not matter if you by from a dealer or individual, you can't legally purchase a handgun in a state that you are not a resident of. There are other state laws for some to consider, if you were a resident of Ca. for example, but those do not apply to you.
I too am going to the Louisville show, there is also a Dallas Market Hall show this weekend.