There is a secret online gun store that will literally sell anyone anything.
To access it, you have to use powerful encrypting software.
And you will have to pay in bitcoins.
They will ship your firearm to you in pieces unlikely to draw the attention of the Post Office.
And you will get to do time in a federal prison if the government catches you.
Want drugs too? Same thing with illegal chemical mood enhancers.
The internet is either an amazing resource, or in this case, a great medium for a government sting operation.