The answer is "You can't." It's not possible to run a search of Network candidates as you can with candidates in your account.
The closest way to accomplish this is to add your job, perfect the job's Scoring Criteria (while viewing a job, click Scoring Criteria tab > edit), and let the Recommendations engine run overnight. The next day you'll have available the list of recommended candidates. To view the list, go to Candidate Manager > Recommendations tab and alter the filter if necessary.