Well it's not as if you can just break into any old gun store or rural home and find a select-fire weapon.
Just put a lightning link into your AR style rifle, and voilà, you have a full auto gun.
Pretty sure a lightning link is more "elect-fire", not select-fire. Not to mention much more dangerous than the relatively well documented and simple (highly illegal without an SOT) procedure that can be easily found to do a proper conversion.