On paper, having built stuff for YC startups sounds like you are plugged into an amazing network. So it is a balance of being direct "hey we are taking on new clients!", and a balance of going to events and being more indirect and observant.
Go to events, go to trade shows, be social, make yourself known, write blog articles under the name of your group that they can find you under, and if you can manage it publish some open source code.
All of this sounds way easier and like less time investment than it really is sadly, but it will build your reputation.
But in summary, the consulting gig requires a healthy portion of creative sales skills and other skills, so have fun practicing them all in addition to tech skills.
good luck!
1. Landing page with your names, contact info, and experience/skillset. Answering the usual questions like what kind of work, etc...
2. Email everyone you have worked with or talked to, say "hey hope you don't mind this email, we're available for consulting, here is some more info, do you know anyone that might be interested? If so would you mind sending an intro." Also call some people if you know them well, calling will likely work better than emailing. Trick is: don't ask THEM to hire you, ask them who they know that might want to hire you.
That should get the ball rolling.
I started off similar to you, working predominantly with YC and other incubator startups. Tapping into those existing networks is what kept feeding me with new work.
So leverage what you already have and ask your past clients and their friends for work or even just letting them know you're available to give advice/critiques on what they're doing (that will hopefully lead to contracts after you’ve shown your ability to solve problems).