Personally, I have way to much competition for jobs where I am. Since I do this as a side job, I am not always available, so I am sure that there are others who have direct contact with schedulers to get shops before they hit the boards, but I have a tough time finding more than a handful of jobs each week. I truly can't afford to say which companies have great jobs near where I live. It is about 90 minutes in any direction to the closest city even approaching 100,000, so that comes into play.
It is work to sign up for companies, but that is part of the cost of doing any business. Most people in business won't hand over a list of their best leads to their competitor.
When I think of my best shops both as ranked by pay and by enjoyment of the experience, they both came from companies I had been signed up with for many years when I got an email asking for assistance getting them completed. They were my first jobs with either company.
If you have questions about a specific company or how to do a specific shop, I will answer those questions when I am able.
I know you mentioned being busy, but it really see it as valuable to take the time to sign up with a variety of companies. When I started MSing, I was working full time as a teacher which included 5 weeks of summer school, working on my Master's degree, and had 2 kids in high school sports. Free time was not a luxury I had, but the money paid for grad school.