Did you even READ your post. If they are obtained illegally already, what are more laws going to do? Make it MORE illegal? I've bought a lot of guns online, and every single one of them had to be shipped to a licensed gun dealer and all of the necessary paperwork done by the dealer, for which I was required to pay the dealer for his time.
Believe it or not, outside of the states that have succumbed to the liberal insanity, most states allow their citizens to sell their privately owned firearms to other citizens as long as they believe that the other person may legally own them in that state. Guess what? These are the states with the LOWEST violent crime rates.