Getting companies to contract you out to build a program for them can be difficult without either completed projects you have done to point back to and show the quality of work you can do or having someone "talk you up" or otherwise recommend you for what a company wants done. While sometimes difficult it is not impossible by any stretch of the imagination. But to get to the main point of your question.
There are many ways, aside from being networked and knowing people, to find companies who need programs of varying sizes made. One site is called www.GetAFreeLancer.com"I found this site in about 10 seconds by searching google, i'm sure there are much better sites out there this is just an example".
Aside from sites to find companies looking for someone to make a program for them, there is also the option of learning about some companies, going up to them, and pitching a software idea you have that you think they could use. I would also highly suggest making a web page that you could use to attract companies by having your business info on it, including what languages you program in and some examples of the work you've done. Also, as posted in The TXI's answer, once you've done a job for a company you can go to similar businesses and pitch the software to them so that your essentially just modifying (if not just straight up reselling) software you've already completely built and debugged.
Given all of this, here is my advise to you: Take the job at the smaller company while also starting your own business part time. That way you can built up your customer base while also still having a steady income as well as having co-workers who can help you out by pointing you towards companies that might need programs built as well as maybe even finding a programmer or two that might want to join your new business.
EX: I'm am currently in a computer business where we can do software, websites, and fixing/building computers (as a part-time job outside of my regular engineering job) that was started by a friend of mine whom i met while i was a co-op at Michelin.
Every little bit helps and the main thing is you don't want to jump in the water with both feet before you have a decent customer base if you can possibly help it.