There are a few different ways to go about this from trade shows, to directories to working with an agent or rep. We talked about this a while back on our blog and rather then repeat it all, will give you the link to the original article:
http://www.acf-china.com/blog/2008/09/08/sourcing-phase-finding-the-right-supplier-to-manufacture-your-products-in-asia/
Good luck - sourcing the supplier is really just the beginning.