You just have to reach out to people, you can't expect to sustainably rely on referrals for growth. Remember that your existing clients have no incentive at all to refer you to other people and in most cases are disincentivised from doing so. Instead use your success with your existing clients as social proof when approaching other companies in their niche: "we just delivered X, Y and Z to CompanyYouveHeardOf, let's talk" is a great way to open a conversation with those other companies.