Your local gun shop can get them, or you can find them on the internet or gun trading websites.
First, you must make sure that your local police have no objection to you having one. Most do, and that is the first requirement to be issued an ATF transfer stamp. Of course your background must be impeccable and you must buy a very expensive gun safe to keep it in.
The weapon will cost between $2000 and $10,000 and the permit and licensing, if done by a professional, will add another $1000 to the price.