My original band was looking for a singer a few years back. we posted on Craigslist and sent any applicants instrumental versions of our songs and told them to write new lyrics/melodies just to see 2 major things:
1. if they can sing
2. if they can write
Your case might be a little different, so I'd say you could try Craigslist too, but maybe include in the ad your influences or a few songs you cover and tell them to be ready to sing song A, B, and C when they get to the audition.
Also, Craigslist is hit or miss, so be ready to weed through a few doozies.