Pretty much anywhere you can get it, google and competition would be good starts (competition could be a good idea of a market depending on their success).
Put up a landing page with email sign ups for notification of when product opens.
I'm developing a product targeted at a similar market as LinkedIn, but directed at portfolios. I've been told that it's something very difficult to build a business model on but i still believe in the idea and i'm looking ways to research it. In this case i could data mine LinkedIn for example then.
Are you aware of any reading material about it and guidelines to define pricing and etc?
EDIT: my goal is to elaborate a business plan on it, at least something that could be improved on
