What to do when the door is locked?

I have submitted several direct proposals to companies, and get "we don't work with outside people". Who do they work with then? I understand they may not be in the hunt for new ideas, but I may have something they can make money with. Wow, when that door closes, it's loud. So, I go to the NEXT building! I look up the company's competition and pitch the idea to them. Hopefully someone in the related industry has a contact I could reach. Let me know if you've had any experiences when the door shuts, and you've found another way in. (yes, I'm ending with preposition.)