[alain94040]

The best co-founder is someone you worked with before. Have you really contacted all your [good] ex co-workers to find out where they went? Even the ones who couldn't possibly be interested in startups? People change.

If that doesn't work, network. Once you find someone who seems good and interested in your space, get them on board on a temporary basic. Pay them, do whatever it takes to get them to work with you for a 1-3 months. Only then sign papers that give away significant stock and make them officially a co-founder.