You can trade some of your work for referrals and recommendations.I couldn't find your website so I don't know what you have there, but you can add these to your Linked In profile to start with.
Are these charity barters just one aspect of an otherwise sustainable financial footing for your company? If yes, and your company is financially solid and able to afford to give away services, perhaps you could share how you did that and help your clients get to financial viability sooner rather than later.
Lastly, you might consider a one-to-many approach. That is, you can make videos or create online webinars that deliver your services to several clients at once. That way everyone gets used to paying something, and you start to monetize your valuable expertise in an affordable, repeatable, (not necessarily completely free) way.