Well . .. we have some "independent" brokers/sales people who use us exclusively for all the items they sell . . so we treat them the same as our in house sales people, priority in scheduling and quality they can count on . . . kinda like a freelance sales person for us . . .
so find a shop that produces the work you want to sell and talk to them about a situation like that .. .
If you wish to broker, just know that there will eventually be the inevitable first disaster: customer goes out of business before paying, supplier's shop burns down, etc. It takes a strong stomach to be in business for yourself.
We run a "trade printing" operation and I can tell you wholeheartedly that a good trade supplier, or an
assortment of good trade suppliers, is an excellent way to keep your headaches to a minimum. It's hard enough to profit on sales alone: why bring the problems of machinery and high payroll into the mix, too?
Kringle is right about the satisfaction and higher profit potential of your own production facility, IF you enjoy the non-sales end as well as sales, and if you are trade competent.
If you're just starting off in competence, brokering is a much lower reach to profitability... and you can always start up a production facility later with the money you've made, making sure to follow Kringle's very intelligent guidelines.
As Dabob implies, an intelligently run shop (even if it isn't a "trade only" shop) will understand that you as a broker are a REALLY valuable source of work. The biggest challenges are finding a place that can produce what you want and who won't steal your customers.