OK, I think the piece you are referring to is called the action on which the trigger and barrel attach and houses the bolt. That is the heart of the rifle. If you do not have this piece you will have to find a used rifle to act as a donor or possibly find one on the internet. You may have some luck finding one in a pawn shop. Since the 722 was replaced by the 700 in 1962 it has been the most widely cloned commercial action. No one to my knowledge machines the 722 action.