Most of the data is collected from publicly available company websites from yahoo directory.

In that case is it legal to call company numbers and ask to speak to somebody in the related division.

I think I will start with adwords once I somehow signup 100 beta customers talking to them at a personal level.(Linked In might be a good way.) I will keep some free promotion to these intial 100 customers to encourage them to send invites to others for signing up.

Regular Mail marketing is also something I will have to try. This is a very niche field but I will look up if they have some related magazines in which I could advertise.

Trade shows may be expensive for me in the beginning.

Thanks for your suggestions.