It would be really awesome if YC put on some type of match-making event for single founders to find co-founders in person. Like a speed dating event for startups.
I feel like that would be somewhat counter-productive for YC.
They're looking for people who are going to be Flexible and Determined to make the startup happen, regardless of what obstacles get thrown in the way. Finding a co-founder is one of the first real obstacles, and will definitely not be the hardest one over the life of the startup. By exemplifying the qualities listed in this essay, a single founder should be able to find at least one solid co-founder.