What is a useful way to find initial customers for a B2B product? (As other commenters have noted, mTurk is more useful in a consumer setting.)

Is there a way to find initial customers in a scalable manner? i.e. scaling it across many different business ideas and potential customers?

This would be a great service that a lot of people would pay for. I know, I know, I'm asking for marketing to be commoditized and turned into a service, which is hard. I don't really know how to do it.