only at "gun shows"
In most of the US, they are legal. However, it will depend on the type of gun, and exactly where you are located. We get questions from several countries, and the list is far too broad to post here.
Commercial or private?
probably
It's not legal.
From a New York gun dealer.
Short answer- you don't. Like most of the US, there is no requirement nor means to register ordinary firearms to any one person. Private face-to-face sales of firearms are legal between private parties if both reside in Utah.
This depends on your state's laws, but federally, so long as all the sales are private (not dealers) and do not cross state lines, this would be legal.
n0
Anywhere it is legal. Your local police and gun shop can help you.
No. New York bans them just like they ban machineguns / full autos.
A private sale (legal in most of the US) is when one private citizen sells a gun to another private citizen. Both must be from the same state. This is opposed to a sale that involves a firearms dealer. Example- my neighbor and I hunt together. He likes a shotgun I have, and wants to buy it from me. He gives me the money, and I give him the shotgun.
Try gun shops, pawn shops, want ads, for sale ads, gun shows, estate sales, yard sales, garage sales.