have a look here:
http://news.ycombinator.com/item?id=1052950
and do a google search for
site:news.ycombinator.com co-founder wanted
and
site:news.ycombinator.com looking for a co-founder
best of luck!
http://socialstrategist.com/2008/04/16/your-users-are-boring...
HN did start a cofounder wishlist GoogleDoc a while back.
You can find it in a more searchable format on http://StartupLinkup.com
Write up an Ask HN post about your project or idea and ask for feedback and then maybe at the end say that you're looking for someone to help with it as a partner. Or something along those lines.
As much as we'd wish HN to be a different type of community, this is still an online community and you can only know the next HN'er as much as anyone knows anybody else from an online community. However, when you discuss things of a non-superficial nature then you'd get to have a feel of the other person's personality.