Walter found everyone else. Happy found Walter.
He was on the side of the road, in his broken down car. She pulled over and offered to help him, he gratefully accepted, mentioned that he was getting a new one as soon as he could afford it. Talking to him while repairing the car, they recognized each other for what they were. Geniuses.
Walter had to run, he was late meeting Megan. However, he told Happy to drop by the Scorpion office the next day, and he would explain more then. Seeing the possibilities the mechanical prodigy could bring to the table, Walter wanted and needed her on the team.
When she dropped by the next day, Sylvester was at his chalk board and didn't even notice her arrival. Walter was at his computer, and a messy third desk with some vintage records was off to the side. He told her about Scorpion, his dreams for it, etc. She saw the possibilities and agreed to join.
Walter never got a new car. It was too big to fit into his box, and he couldn't justify buying a new one when Happy was around and didn't mind fixing it for free. He wouldn't have met her unless his car was crap.
It was his talisman for Happy.