Any advice on getting into freelance illustration?

Answer 1

Contact

Print Media Service or Metro Creative Graphics

They are both clip art services that will freelance jobs.
You can get their addresses online. They'll have requirements and what they want to see as examples.

Answer 2

You probably could contact a school; such as Art Institute to find out if they have a list of companies needing freelance illustrators. Otherwise you could check it out on the net. type in art and define it into smaller categories till you get to freelance illustrator.
I hope this was a help
GramSam