Lead is right, most agencies have dive job listings on their respectiv web-sites. PADI and NAUI are no exception to this.
Then there is what I believe is most practical, once you are an instructor, contacting shops in person in the area you are in or will be in allows them to meet you, by then, you'll have your resume hammered out as well.
Now, depending on where you go do your IDC, many of those ops have a pseudo-placement program. This will help you as well.
What do dive ops look for? Besides the obvious credentials and insurance, competance in teaching as well as a "people person".
Now a word of caution, if your looking to make a living in instructing, know that a very small percentage of instructors actually do THAT. Many of us have what I call "real jobs" that pay the bills, and teaching diving essentially pays for our trips and toys.
Keep this in mind...