My company helps tech startups reach the prototype phase so they can validate their market and begin iterating. We have worked with a couple "green" startups, but we have no way of generating those leads specifically.
We'd like to focus more on startups that help in some way, like sustainably providing services to the poor, or improving the environment, for example.
If you were looking for these kinds of startups, where would you look?
I would be blogging, twittering, etc. about social entrepreneurship. Check out LinkedIn Q&A as well as Groups. Start your own group on there. Build your own community around this, start a Ning network.
Attend tech conferences that focus on social change. Better yet try and speak at those conferences.
Try writing guest posts on various tech and startup sites.
Get your info out to organizations that first time entrepreneurs might go to for help or advice like the SBA, Chambers, Colleges, etc.