There are probably too many ways to respond to this question without making a full post, but a few examples:
1 - Reach out to other freelancers - many freelancers actually have too much work and will refer some leads along to others they trust.
2 - Recruiters - find an agency recruiter who you can trust and tell them to keep an eye out for you. Recruiters love placing contractors, as it is basically an annuity revenue stream.
3 - General outreach - just reach out to people. Founders, meetup leaders, CTOs. Do a little research and send short messages declaring your availability and interest.
4 - Let the work find you - make sure you have a discoverable presence on LinkedIn and elsewhere.
I have a LinkedIn presence with solid skills and I'm absolutely bombarded with full time roles. Even though I have consultant plastered all over the title and profile, and even though I'm currently in a consulting gig, and even though I'm freelancing under my own company, I get almost no consulting gig (that don't pay lower than full-time) recruiters reaching.
I'll actually pay a finder's fee to those who find me consulting gigs (ones that pay senior rates). LinkedIn isn't working for me, here.
edit: source: I was a hiring manager in a past role and I learned the real take-home pay of the consulting agencies when they farm out consultants.