Whats the lowest level you can get a purple rocket launcher at?

i tried to use a bunch of keys on a level 1 character but box items were lvl 7 and no rocket launchers so what level do i need to be for them to start showing up in TPS?

They should show up at level 7. Im sure ive had them before but they may be quit rare. Also the lowest level loot from the chest is level 7.