I've met several. Anticipating what you might ask, what makes them 10x engineers? The ability to go off by themselves, get themselves into a type of trance because they are so focused and return a week or two later with thousands of lines of a fully formed formed program with near perfect working code. It's amazing to see.
A fair few, yes. Don't forget that the original definition (from Peopleware) means that these engineers are 10× better than the least capable engineers who are able to maintain their career, not 10× better than the average engineer. They were also comparing engineers across companies, so it's possible (though statistically unlikely) that you and every engineer at your company are 10× engineers.
Sure, I've met them. I've been them. I've also met and been the opposite.<p>Many people can be 10x when everything is aligned for their specific skill set, working environment, and personality. Being hyper-productive is less of a unique aspect of a person, and more about giving people the exact environment in which they can do their best work.