I don't think your question is clear. Are you asking about a contractor bidding on jobs that others have designed? (You would need to be credentialed and have, or develop, a relationship with designers.) ... or a designer looking for leads for design jobs? (In which case you would need credentials and to develop relationships with clients ... where and however you can find them.) I don't know of any online place where you could develop or purchase leads to gain clients. What you might be after probably falls somewhere between some form of networking and advertising.