No, you can't. Any weapon purchased online must be shipped. The only shipper I am aware of that will ship firearms is UPS. They are required to pick up the firearm to be shipped from an FFL certified dealer. The firearm must be shipped to another FFL certified dealer chosen by the buyer. The buyer then must complete all paperwork and pass the instant background check before being allowed to take his firearm home. The only way to buy online the way you describe is if it is a private owner and he lives close enough that you can meet in person for the transaction. That is a legal transaction.