Reach out to people in your network, people you know online, or just people that are associated with the industry. The further they are away from a personal relationship with you they are, the harder the testimonial will be to come by, so figure out who you know and take them out to lunch. Tell them that you are looking for their feedback and take the good feedback and ask them if they can quote them on what they said. Most of the time, face to face, they will say yes.