It’s very difficult to do it without a firm or agency to seek contracts for you. Basically, you have to start at the bottom, scraping bedrock, accepting anything and everything that’s offered to you. Then you meet one guy. Just one guy. And it’s usually an accident, or a coincidence. But you meet him, and he’s impressed, and he knows a guy. And from there, the ducks start lining up.
You get hired for a job, and you do well. Then you get repeat business, and recommendations to people. Then you start having enough money to invest in yourself. Fancy certifications that make you stand out on paper, and the like.
Basically, if you’re starting out, you have to get a GREAT business card, and stretch the truth to the point of almost breaking it to make yourself look good. And with time and effort, comes the payoff.