Self-tapping machine screws are available at hardware, home supply, and auto parts stores. These screws are also available at online industrial supply warehouses and websites that specialize in fasteners.
Home supply and improvement stores such as Home Depot have extensive collections of screws. Self-tapping machine screws are sold in the hardware section and can be purchased in bulk. Online fastener suppliers, such as Hillco Fasteners, sell a variety of self-tapping machine screws with various head and shaft sizes. Online industrial supply warehouses, such as Grainger, also sell these screws. Additionally, marketplace sites such as Amazon.com often have extensive tool and fastener sections.
Self-tapping machine screws and self-tapping sheet metal screws are not the same thing, and self-tapping sheet metal screws are much more common. Self-tapping machine screws are screws that have cutting threads on part of the shaft, whereas their sheet metal counterparts have cutting edges along the entire shaft. This means that these machine screws bore partway into the machine into which they are drilled. They do not cut new threads when they are removed and reinserted. Rather, they follow the thread path of the first cut hole. Self-tapping sheet metal screws bore a new hole each time they are screwed into a material, and have completely different uses.