This site should have most job listings.
This site will be where job openings are discussed candidly (and usually, though not always, anonymously) by the true industry insiders.
That said, these are just a starting point. The real place to be is your own network of contacts. Most job openings can expect several dozen applicants at a bare minimum, and sometimes the count goes into the hundreds. That's a lot of work for a sports editor just to pick through them, so often jobs aren't being formally advertised. It's a small business, and people know who is good and who isn't. Make sure they know you.