Where can you find postings of job opportunities for nurse practitioners?

I do not know your exact location but wherever you are there are lots of job opportunities for nurse practitioners posted in quite a lot of internet websites. Just search for "nursing jobs (specify your location) and you will get handful of results.

Newspapers
The individual local hospital's websites
Hospitals themselves.
in a hospital
I see them in the paper locally all of them time...usually weekly (nashville)
Try this out yahoo jobs. It will give you a list of job openings for nurses according to state.
Websites of newspapers, which can give you the job opportunities in places from which it might not be easy to get the paper promptly.
try http://www.ajb.dni.us/

America's Job Bank.. they have millions of jobs listed, should be one that suits what you are looking for. :) hope that helps.