The toughest part is not finding the people. The toughest part is getting them to be real. When marketing advice is just a blog away, most people you “test” your design with will put on a marketing hat and try to say what an expert would say. That’s of little use to you.
You need them to act like your customers would act. Don’t ask, “What do you think of this?” Set the scene properly. “You’re a really busy engineer. What would you do if one of your staff put this on your desk?” Or “What would you click on next?”
Jakob Nielsen says that testing with five people will reveal 85% of the usability problems in your design. He means five real people.