It's pretty hard (even if you are a great programmer). If you are looking to find a great programmer who's available long-term, hire someone who's PROVABLY great and available short-term to do the interviews/search for you. Think Stroustrup or Stepanov if you are looking for C++ programmers. RMS or Steele if you are looking for Lisp programmers, etc.

For every good programmer I know, I know many more who are total bozos who claim to be great and are thought by some to be great.