Sounds like you have the basics right -- a quality team that can deliver solutions. I think you'll find better "referral" opportunities on your own, using data and some smart content marketing.
Start with what you do best. Create content showcasing problems or pains you've solved for your clients. If you can get permission, show your client brands and video testimonials. This can also be published to your owned domain (blog) to build up search equity. Once you've built your content hub, you'll need to explore some paid promotion. We're not talking thousands--experiment with small amounts to figure out what works best.
Here are some ideas to explore:
1) Consider using LinkedIn paid ads, using your existing client base as your targeting or modeling criteria. Like Facebook, you can use an existing client email list to target similar potential customers. Use pre-recorded testimonial videos as the ad content, as these past clients are probably known names in your area.
2) Explore doing likewise on Facebook. See above.
3)Tabula, Outbrain or other native distribution networks are offering some great options.
If your promotion budget is on the bootstrap level, give email marketing a try. This is also one way to reduce the friction for referrals.
Here is a high level outline of how to set up a n email referral program:
2) Set up an appropriate incentive. It could be "winner chooses a charity to get a donation" or something as simple as "win an iPad". You could also do something more on brand, such as give away tickets to a local film festival.
3) The last step might require some technical help, but basically when a client clicks on your email, you'll want to track the referrals they enter. If any result in new business, you'll want to acknowledge it appropriately, and also deliver on your prize.
A more simple version of the above would be to include copy in the email that invites your clients to forward to s friend. You'll just need to figure out how to track who referred who.
You might be doing this already, but consider submitting some of your work to awards or other contests. Every marketing manager loves getting the recognition for their "work", and they'll be more likely to share with their network. Basically, give your clients good reasons to share and be excited about your work.