Hard to find silicon bronze nylon insert lock nuts, commonly called nyloc nuts are found right here at Fair Wind Fasteners.
Made of a guaranteed 655 silicon bronze alloy, with a nylon insert that has an inner diameter that is slightly smaller than the major diameter of your bolt's threads, locking this nut in to place and securing your fastener against coming undone due to vibration. Nyloc (nylock) nuts are known to be far more secure than lock washers.