Free markets often lead to paying markets so do both.
1) most of us don't have columns, we submit stuff and the editor agrees to take it.
2) read the papers and magazines and look to see what's in there --then ask yourself, can I write that? Can I write better than that? Do the research on how to submit for that publication --look in the contact us section and submission requirements and writer submissions --usually burried in the business section of the web site of the periodical or newspaper
3) submit locally first, save your very best for big fish but submit.
4) Determine which places your pieces fit best --magazine, newspaper, periodical
5) Guest columns in the newspaper are free. Most smaller papers don't have a budget for free lance unsolicited stuff, but it looks good on the resume. I have submitted and had two freebie columms in my hometown paper just to keep me writing.
Other than that, look in the paying markets of AW, and at the bio lines of people in the humor section, and look in goals and announcements -- at where other people have had success. Then PM them and ask how they got published.
Good luck.