Several years ago, I found out about the Artists & Graphic Designers Market resource book. It comes out annually and lists companies in different businesses (book publishers, greeting cards, etc). It gives a brief description of the company, what they are looking for, who to contact, etc.
I would always either check for a website/email or send a letter with a self addressed stamped envelope requesting submission procedures. To those who responded, I would send a large portfolio of my work plus return package & postage. $20 and sometimes months later, I would usually get a thanks but no thanks reply.
Finally I decided to just send out brochures. So I made a small 5x5 brochure with 8 pages. It fit perfectly in a CD envelope which also had a big round window. I included a SAS postcard for a reply. I made sure to include the return address of where I sent it so that I knew who replied. Oft times they would just write a quick note and I would have to guess who returned it.
I sent about a dozen out to the artist representatives that were listed in the A&GDM book. Got alot of thanks but no thanks. But Wilkinsons replied that they liked my style and said they would keep the brochure on file.
Several months later, I got a call from them to get my approval to submit my work to a client for a project. I was not the only artist they were showing the client, but one of many.
They sent a contract allowing them to use my brochure. I signed it and sent it back. Didnt hear any more.
Several months later, same thing. Do we have your permission to submit your work to a client. Made some changes to the contract and sent it on. Didnt hear anything.
Several months after that, I get a call about another project coming up. It then occurred to me that they were only submitting my little brochure to the client -- that they didnt have access to my portfolio.
So I sent a copy of my portfolio and a few months later I got my first freelance project. I did a couple more and then was asked if I would want to be fully represented.